Dan

There are adhesives available that are safe enough for bathrooms. The problem is with cement based adhesives for walls it this, A) if it's cement V plaster, you have to prime it, the cement and plaster don't mix well and bond can become free in the future B) cement based adhesive are not waterproof, they're water resistant, so they allow water to pass through them and they don't break down, but the plaster or plasterboard behind will and can.

I suppose providing you can tank the shower / bath area though, and prime the rest (if plaster), you'd be fine.

In my opinion.