I agree with the premise, and would have used ios-simulator if I'd been the first to create the tags, but don't ignore the fact that iphone-simulator has 1,012 questions, ipad-simulator has 95 questions, and ios-simulator has 29 questions.
Is there any harm in making a distinction between the simulator as used for the iPhone and iPad? This merge would loose the information contained in the previous 1100 applications of that distinction. Sure, they're the same app, and sure, you need to also search for [iphone-simulator] when researching a problem you encounter while using the iOS simulator for the iPad, but it seems a little extreme to merge 1100 questions into a tag with 29 questions.
I'm not opposed to the merge or synonym, but these numbers should be considered.