Transmit? Not legally. Receive only is OK.
It has to do with FCC type certification. That's a complex subject, but it's basically an approval given by the FCC that says the radio meets the specific technical requirements for specific radio services.
The UV-5R transmitter doesn't meet any of those requirements, so it is ONLY legal to use on the amateur radio bands. The FCC has no transmitter requirements on the amateur radio bands, other than some nebulous requirements in the Part 97 rules about not causing harmful interference.
Yeah, we know, tons of people use them on FRS, GMRS, MURS, Marine VHF, public safety, etc. That isn't the same as it being legal. And no, the FCC doesn't have roaming SWAT teams in black helicopters that are going to swoop in and haul him off to lock up.
If your brother wants to be totally legal, the only place he can transmit with them is on the amateur radio bands. Not FRS, not GMRS, not MURS, not anywhere else. There are plenty of radios that DO meet the requirements and have the type certifications that are required.
Baofengs are essentially the scum on the bottom of the barrel after all the other radios are removed. I know they are attractive to some as a low buck entry into the amateur radio hobby, but they should not be confused with suitable radios for any other radio service.