Is it legal for a caregiver to use a Hoyer lift alone in clients home?

What is done in a home is not regulated.
There may be warnings not to use it by yourself but that is a standard warning.
I used a Hoyer Lift at home and I used it by myself. When the CNA from Hospice came there were 2 when he required the use of a Hoyer. But that is the regulation that Hospice had.
I can/could instruct a hired caregiver (privately hired, not through an agency) to give my Husband medication. Again what you do in your home is not regulated. I could put bed rails up on both sides of my Husbands hospital bed...this would be considered a "restraint" in a facility but private homes are not bound by the same rules a facility or hospital is.

If you are a caregiver being paid to provide care in your client's home, you had better check this very important point with your insurer (professional indemnity) and with your client's insurer (home policy, covering injury to third parties). Such insurers will know the law, and even better they will tell you in what circumstances you're covered. It's a useful guide as to whether or not something is a good idea.

If you are employed by an agency, ask your agency/line manager to do the same.

If you are the client or the client's family member wondering whether a caregiver is keeping to real rules or is creating an unnecessary fuss, then you need to check the same points on the caregiver's behalf.

There are two sets of risks:
risk to the client
risk to the caregiver

If the caregiver is not confident that the lift can be used without risk to the client or to him/herself, s/he is right to refuse to operate it.

For academic interest and browsing, here is part of the relevant Health and Safety Code relating to Safe Patient Handling in Nursing Homes and Hospitals. The standards enforced in a domestic setting are, of course, not as stringent; but then again, you wouldn't want the client to be less safe, would you?

Sec. 256.002. REQUIRED SAFE PATIENT HANDLING AND MOVEMENT POLICY. (a) The governing body of a hospital or the quality assurance committee of a nursing home shall adopt and ensure implementation of a policy to identify, assess, and develop strategies to control risk of injury to patients and nurses associated with the lifting, transferring, repositioning, or movement of a patient.
(b) The policy shall establish a process that, at a minimum, includes:
(1) analysis of the risk of injury to both patients and nurses posed by the patient handling needs of the patient populations served by the hospital or nursing home and the physical environment in which patient handling and movement occurs;
(2) education of nurses in the identification, assessment, and control of risks of injury to patients and nurses during patient handling;
(3) evaluation of alternative ways to reduce risks associated with patient handling, including evaluation of equipment and the environment;
(4) restriction, to the extent feasible with existing equipment and aids, of manual patient handling or movement of all or most of a patient's weight to emergency, life-threatening, or otherwise exceptional circumstances;
(5) collaboration with and annual report to the nurse staffing committee;
(6) procedures for nurses to refuse to perform or be involved in patient handling or movement that the nurse believes in good faith will expose a patient or a nurse to an unacceptable risk of injury;
(7) submission of an annual report to the governing body or the quality assurance committee on activities related to the identification, assessment, and development of strategies to control risk of injury to patients and nurses associated with the lifting, transferring, repositioning, or movement of a patient; and
(8) in developing architectural plans for constructing or remodeling a hospital or nursing home or a unit of a hospital or nursing home in which patient handling and movement occurs, consideration of the feasibility of incorporating patient handling equipment or the physical space and construction design needed to incorporate that equipment at a later date.

I also found this. Again it relates to nursing homes and other regulated settings, but again it just as well be applied to a family home.

Texas SB 1525. June 17, 2005. (not room for text so I've just included the link) http://www.capitol.state.tx.us/tlodocs/79R/billtext/html/SB01525F.htm

I don’t know if it’s legal or not, but three different home-health agencies only had 1 caregiver moving my mom. I’m in GA.

I can't imagine it would be required that 2 caregivers always be available in home to operate a Hoyer lift. Who on earth could afford that? How would any disabled people be able to remain in their homes? One sensible person with thorough training is fine. That's the whole point, the beauty, of the Hoyer. I operate it in flip flops while thinking about what I'm going to have for lunch, with National Public Radio blaring in the background and and perhaps also an important sporting event on the TV. It's fine.

SnoopyLove I preferred using the lift by myself, too. Not least because I found having another person was a distraction that stressed me out when I wanted to focus on my obsessive-compulsive strap-checking routine.

But you are and I was caring for our own parent. If we dropped him or her, or knocked ourselves out on the crossbar, or swung their foot into a cupboard door and broke a toe, then our heads be it. It isn't the same when a paid professional is in the house.