Unless they are free, no, not really of use.
As BFL13 has mentioned, most AGMs that are designed for UPS usage are not going to hold up well. Those batteries are designed to be constantly charged and only intermittently discharged.
If they are free, take them and get what use you can get out of them until dead..
Most companies will change out UPS batteries as part of the maintenance to ensure their systems will have the max up time as possible during short duration power outages.
Typically 2 yrs then swap out the old with new batteries.. If you can get them during a swap out, good chance they will still be fine for a couple of years usage but don't expect them to live long.
I wouldn't recommend paying for them or buying new UPS AGMs for a RV, just throwing out your money if you are planning to do so.
Best bang for the buck is the 6V GC2 FLAs you can get at Sam's or Coscos if you are looking for a bargain..
Sam's also sells a AGM 6V GC2 battery, typically runs about $15 each more than FLA but you get less capacity if AGM is what you are into..