Sounds like the bigger issue here may be "employee vs I.C." and which one are you?
Referral fees are not the same as ongoing commissions, and commission is not necessarily the same as a "kickback." Plus some states define it differently.
It's a little different scenario if he is paying you a reduced fee to temporarily see her client (you could say no) or asking you to pay her every time you see a client that has formerly seen her.
If these are clients that she is retaining, and you are seeing them once in awhile or temporarily, it is similar to paying a fee to stand in (Independent contractor.) For instance: business takes in $70 for the client, you receive a $50 fee, business keeps $20. In that scenario though, the primary business should be taking the money in, and then paying you your fees on a 1099.
2nd scenario: your rental contract is $xx/month, plus x% of income generated from these sources and x% of income generated from those sources. You would have the right to weight your income sources as your schedule allows: deciding to take more or less of the higher % opportunities as you see fit.
3rd scenario: your rental is $xx/month, plus x% of ALL session income as a fee that covers wear and tear, maintenance, advertising, utilities...
All of these are perfectly legal, and perfectly normal ways of doing business, unless your state regs specifically has something to say about this.
4th scenario: you rent for $xx/month. Your contract says nothing about splits and commissions. Your landlord tells you that your continued rental is now contingent upon you paying for the "privilege" of serving his clients, and you will not be able to say "no thank you," or else you will be asked to leave.
This would be not only unethical, but very likely illegal on his part.
5th scenario: you approach your landlord, tell him that if he will refer you anyone that you can bill their PIP insurance, you will cut him 20% "referral fee." This is a kickback. The arrangement would be based on fee for referral, the referral would likely not happen without the monetary incentive to the referrer, AND you are involving insurance or a 3rd party pay. Illegal.
As far as HIPAA, some states automatically include massage therapists as covered providers. Some do not. In many states, a massage client's PHI (private health information) is only legally covered if they are seeking massage under a HCP's supervision, if a prescription is involved and/or if you are billing insurance. In many states, if the client is self-referred, a cash client, seeking relaxation or spa massage, or any "elective" massage therapy for "recreation," you can legally buy or sell their information in any way you choose. I'm speaking only of legality, not personal ethics.