So.. the strings on my acoustic are totally dead, I haven't played it in forever. My sister has been playing it, and the strings are about a year old.

I have an extra pack of GHS that I won't use on my electric because I prefer D'addarios/Ernie Balls.

Will the pack of GHS be ok on acoustic? I don't see why they wouldn't be, they're just strings... but are they meant for only electric, and if they are, why?

They wouldn't sound like normal acoustic strings, but the real question is if the guage is too light or too heavy.
I think string are pretty much universal in anyway other than from bass to guitar or guitar to bass. But those strings should work on an electric. may not be the best type of strings for an electric but they'll work.