I don't see a reason why not. Granted, chances are that we'll also suggest the official app, but we've always found it awesome when people build great stuff with (or without) our API, and we've always said so aloud.
I would rather not
pull a twitter suddenly say "Oh, people are building cool things with our API? Great, let's destroy them all!"
Of course the mere fact that we control both sides of the pipe can give our own app a certain advantage (e.g. right now we're building the write-API alongside with the app, and thus have a pretty big head-start), and the simple fact that it's the official app tends to give you advantages as well.
But at the end of the day, we'd rather compete on merit; in other words, we'd prefer that people use our app because they like it, and not because we fail to acknowledge that there's a whole bunch of awesome apps and tools out there. After all, the developers of those apps are helping us as well, both by promoting our sites, and by helping to refine and improve the API.