Buy wireless mike from different vendor?

Hello

This question really belongs to the Hardware section but there's none about microphones.

Someone I know uses hardware from Audio Technica to provide sound for conferences: ATW-R14 as the wireless receiver hooked up to a loudspeaker, and a single ATW-T52 microphone.

I was wondering if wireless receivers can be used with other brands of microphones, or if they use some proprietary communication protocol that requires buying wireless microphones from the same vendor?

Also, am I correct in understanding that the receiver accepts up to two wireless microphones?
Thank you.