I assume by swing you mean using snappings like 1/3? Definitely legal.
I recommend reading this to get an idea of how intense the map can be
help/wiki/Ranking_Criteria/osu%21taikoAlthough I'll give you an overview of how much 1/3 you can generally use per difficulty (from my perspective):
Kantan/Easy: pretty much never
Futsuu/Normal: bad idea to use notes that are 1/3 away from each other, you'll very rarely see a song that can justify it.
Muzukashii/Hard: if the song has 1/3 you can use double notes, but be careful about it, provide adequate breaks. In very rare circumstances maybe four notes in a row can be acceptable.
Oni/Insane: Probably refrain from using more than 7 in a row. (longer ones can sometimes work, but don't make it too complex)
Anything Above: you can mostly go wild.