Are actual medicals required for MEWP operators or is this a specific company requirement?

If so what would be the frequency requirement?

As stated previously it is good practice. You should be following BS 8460:2017 Code of Practice for the Safe Use of MEWPs. In which it states the below:

'Employers should consider whether those employed for tasks associated with the safe use of MEWPs are medically fit for work.

Note 1: It is good practice for those operating and maintaining MEWPs to undergo suitable fitness and well-being assessment before employment and subsequently at periodic intervals.

An employee's medical fitness should also be assessed after sickness or an accident to identify any possible effect of the illness or injury and treatment on the individual's current and future ability to operate he MEWP safely. Employers should have a system in place requiring employees to report any medical condition, treatment or medication that could affect safety when operating a MEWP.

Each person's fitness for operating or performing maintenance should be judged individually. Some diabled workers have developed skills which compensate for their disability, but their competence in an emergency situation should be considered and recorded in the emergency arrangements.'

I hope that helps.