Can a *reviewer* ask for the status of the paper that is reviewing?
In my opinion, it is ok to ask politely about anything to the editors, as long as you can (and do) explain sensibly why you ask, and as long as you don't demand it. Such requests shall be at worst considered odd or unusual.

In this case, I think it is in the best interest of everyone involved for you to let know the editor about your timing issue (and the sooner the better). The most probable outcome is that the editor will still wait for the second reviewer, because otherwise the authors could think answering your demands should be enough to get their paper accepted, and they could get pissed off if other demands arrive later from the second referee. Even if there is no such misunderstanding, they could prefer to dive in their paper to correct it once rather than twice. 

However, letting the editor know might prompt her or him to push a bit the second reviewer, possibly speeding up the process a bit. He or she might also decide to go with your sole report. In any case, once the editor have all relevant info on her or his hand, he or she can choose the most appropriate course of action.