Q: Can a gmail.com email used as an Apple ID be used to control devices via HomeKit?

We have a situation of two users. One of which already uses an iCloud address as their Apple ID. The other user has a gmail.com as their Apple ID. In terms of using HomeKit (controlling devices, etc), is the gmail account acceptable to control lights, etc in the same way as the iCloud address?.. Or, is an iCloud address required to be an Apple ID to do so?

If the latter, can an Apple ID be changed from gmail to iCloud?

Thank you!

Craig