Can I wear my Apple Watch during hot yoga?
No. Apple Watch should not be worn during hot yoga.
Whilst Other would be the most appropriate activity type for recording regular yoga using the Workout app, wearing your watch during hot yoga (which is performed in hot and humid conditions) would fall outside of Apple's handling guidelines for your Apple Watch.
Apple's advises that:
Note that using your watch outside of Apple's handling guidelines may render your watch ineligible for service under warranty, AppleCare+ and/or chargeable repair service.