No, a ring group (RG) does not hold callers in suspense. If all members of a ring group are busy or otherwise unavailable, the ring will execute the destination rule in order to move the call along.
If all agents are busy, then a call queue is the function that will hold callers in suspense pending the designated timeout being reached or an agent becoming available, whichever comes first.
In a RG, the MOH will only replace what would normally be a ring back tone. Its purpose is to provide some form of sound so that the caller is not hearing dead air and knows that the call has not been disconnected and is still progressing. So it may play for a few seconds or for a longer period depending on when a member answers (if they do) or if it goes to the set destination if established and no one answers.