I would think not, and for a few reasons.

First of all, Survivor should theoretically provide all available safeties and service for all participants since there is a lot of legal issues that can arise from having this type of survival based challenges. They can be liable if they don't take certain precautions and they must be able to aid the members when they need it, or be liable for failing their duty of care if someone doesn't reach out to them.

Which leads to my second point. Making participants pay for any medical treatment on the island may be a deterrent for them to come forth and address any medical issues. For example, rather than being forthcoming about infections caused on the island, they may choose to hide it because they don't want to have to pay for treatment and forfeit the $1 mil prize.

Thirdly, it can be a deterrent for people when applying for the show, since medical fees can end up being very high, and the likelihood for injury is heightened in that sort of situation. This is a big deal for CBS because they want the most possible applicants to have the best selection for their seasons, especially when they do themed seasons such as BvBvB or they want participants with an interesting back story (that may not involve being rich or having enough money to pay for medical fees).

Lastly, I think that because it's hard to get legal approval for doing Survivor, having the ability to provide all-round and safe medical safety, this plays into getting legal approval.

People can also lie about having enough money to pay for medical fees to be able to go into the show, and it may also cause them to have backlash for things like this from the public.

But I'm not sure, I'd be pretty interesting to find out.