I wanted to use a new Dragon mod now that Dragons Diversified is borked. I'm looking at Deadly Dragons, but I'm hearing from others that DD is notorious for causing bloat. Can anyone corroborate or dispute that?

Not sure how well versed you are on what "save bloat" is, it is only bloat if save file sizes jump in astronomical increments (e.g. from a 10MB save to a 100MB after a short play period), and small fluctuation are to be expected.

I can guarantee that it doesn't and that any claims of bloat or bugs you may read are unsubstantiated. Any "bloat" that players are experiencing are coming from other sources, or for mods that have been removed from a game, which is not supported by Bethesda or the game engine.