Probably not anymore dishonorable than being 5 pieces down, and claiming a "win" with .1 seconds on the clock.
Dishonorable to flag in bullet?

You thought for almost 5 seconds and missed 17.Nf7?
hehe
Impressive speed though. Of course winning this way is ok in 1 minute games. That's what bullet is all about.
Personally, I play bullet for the adrenaline and the thrill of speed calculating, doing intuitive unsound sacrifices, and sneaking in scummy wins. It's a great game to play on the metro too. If I wanted to play objectively good chess, I would be playing different time controls.