While it is not completely impossible that a hotel might have a hidden camera installed in the bathroom, it is extremely unlikely that management or staff would place one there. There are strong laws against placing cameras in any area where someone has a reasonable expectation of privacy.
Hidden camera laws vary by state, but all states have laws against property owners placing hidden cameras in bathrooms and bedrooms. Laws generally regard the entirety of a hotel room as being a place where there is a reasonable expectation of privacy. Aside from facing criminal charges, a hotel operator caught in such an act would also face a massive business backlash if it became public.