He wasn't even an everyday player last year, strictly speaking. He earned an everyday spot by about mid July, but that seems to be the way the Angels go, shuffling the lineup constantly. This year it's- one person comes back, another goes on the DL. The other day when they recalled Kendrick, they put Maicer Izturis on the DL. I think they did the same when they brought Figgins back earlier this year.
If Rivera can get healthy, they'll get him some at bats. If they can find an excuse to give another player with a minor injury a two to three week breather that they may not have needed, he stands a better chance for consistent playing time. It's a crowded outfield in LA though, so if your question is:
Now I have another player I can DL if I just drop Rivera outright. Do you think I might as well do it to clear the roster space?
then my answer is yes.
But if you have a free DL spot, go ahead and hang onto him.