Who would be liable for this medical visit?

This is probably a question for your brother’s business lawyer. If he doesn’t have a lawyer, he needed to get one weeks, months, or years ago, before something like this happened.

This is a very sticky situation which could go either way. It’s not something you will get a solid answer from here, as such a judgment may need to be made by an actual judge. I highly recommend you tell your brother to talk with his company lawyer about this.

My brother offered to pay the bills but the guy declined. Not sure if the guy was being nice or planning on sueing.

Could be either. The wisest action now is to lawyer up.

I am not an attorney but one thing seems clear to me. Your brother’s company is not involved since the homeowner made a private deal with one of the workers and it was to take place AFTER work hours. Personally, I think the homeowner is responsible if the possibility of poison oak was never discussed. It certainly was NOT the fault of the worker that he could not identify poison oak. HOWEVER, the poor guy might have to sue the homeowner to get his money.

I’m not an attorney either, but I have the same thoughts as you do. Hopefully nothing will come of it, but we seem to be in a sue happy environment.