Some do, like our system and the Heng Long system. Others will have external receivers.
Pretty much the motherboards are a bunch of ESCs if you want to think of it that way. Some systems (I believe elevation is handled via servo) will use different connections but brushed motors run the main tracks, turret rotation, and airsoft firing if you have an airsoft tank. IR systems are not interchangeable at this time. Brand vs Brand is good, but to do multiple systems you will need something like MAKO2 from RCTA or you will need to swap to that motherboard (or compatible brand) to do IR battles. Some tank clubs also have standards and rules as well.