FRS/GMRS is a set of frequencies set aside for the purpose of making radios like this. That's not a snarky answer, it's just literally all that means. Unless a transmission is encrypted (which is rare) any radio that can transmit/receive on one of those frequencies can usually talk to any other, regardless of brand.
You can find a list of those frequencies here:
wiki.radioreference.com
FRS/GMRS are the same basic technology (FM transceivers) but differ in power, plus GMRS has a few more frequencies allocated to it. So an FRS radio on channel 7 can talk to a GMRS radio on channel 7 or an "FM transceiver on frequency 462.7125". The only difference is that the GMRS or other radios can use higher transmit power so they get longer range.
To use this higher power you need a license, but it's easy to get. There's no test, just a registration fee ($70 for ten years, and they just cut it in half but I can't remember when the cut goes into effect) and an online form. Obviously you're expected to follow the laws such as knowing different channels allow different power levels. But all of the off the shelf radios I'm aware of will do this automatically anyway, so it's not hard to comply with. And the license covers your entire family so it's a bargain.
Most of the folks I hunt or off-road with seem to like Midland radios for in-vehicle mounts, Baofeng UV-5R's for a "cheap option to keep on the picnic table" (they're like $25) and Motorola Talkabouts for a "grab and go" (the guy who hops out to help pick a line down a tricky rockfall, or if we rent vehicles somewhere on vacation). All these radios can talk to each other. I can't make promises on the Rhino because I never owned one, but I just Googled their site and it says it's FRS/GMRS so it probably will be fine.