Technically speaking, you're not allowed to do anything while grappled except what's listed in the PHB. So no activating magic items, for instance. However, our group allows it in our campaigns; being grappled often really sucks, and having wizzes be the only ones who can teleport out seems a bit unfair.
It just seems silly to me that you can poke a guy with a dagger when being grappled, but you just can't seem to remember the command word to use that wand of dimension door your holding in your hand!
It's a spell-like ability with no verbal, somatic, or material components. Since you can cast a spell without somatic components, you should be able to use spell-like abilities.
I don't know what the Con check would be for that, since it doesn't have a spell level ... ?
