No, there's no port of the Game Maker Studio player for 3DS and the source code isn't public. The only reason an unofficial Android port was possible is because there was already a version of GM:S Player for Android.
Nope, it was made with GameMaker Studio. You can confirm it by going to any of the many Undertale datamining websites/subreddits/etc. (and I also made a translation tool a long while ago, by the way =P)
