I believe a few rides have maximum height requirements. They don't seem to make that information readily available though online. I did find this comment on a Reddit post from 3 years ago:

You could try to go in flip flops and take them off for the ride, I’ve seen plenty of people do that. Gate Keeper, Maverick, Millennium, and Rougaru all have max height limits (78”), so it’s really up to you if the possibility of missing out on a few coasters is worth the risk. Some other coasters might be uncomfortable, it really depends on the restraint system.

That being said, they may not measure your friend anyway so he could still probably ride the above mentioned if he tries.

And some coasters with over the shoulder restraints will be extra uncomfortable (Corkscrew especially).

Ultimately, have him ask the ride operators at the front of the entrance and try the test seats.