Yeah, this happened to me all the time ever since I first got Diamond and Pearl. It's okay and who's to judge you? Almost every person who ever used the GTS should have received a hacked Pokemon at one point or another anyway.
You shouldn't use it. If it doesn't fit your team you can release it.
I wouldn't consider it as a cheating, but you should have check it before you trade a pokemon.
I hope you learned a valuable lesson... Never use the GTS.
Why did you care anyways? It was a pokemon just like any other pokemon. If it had something wrong with it, like 999 stats or something, I'd understand, but if it was just a regular pokemon the why does it matter?
It's data. Deal.
Hard work? Who cares about the hard work put into a video game? The end result is what matters. If I traded away a legit lv 100 Lucario for a hacked lv 100 Lucario, I wouldn't care, because besides IVs, etc, it would be no different.