No, you're unfortunately limited to
what iOS provides. I've looked into it a little bit, and it seems that if you want to use a custom font in iOS you need to bundle it with the app and describe it in one of the app's standard config files. So loading it from a skin appears to be a no-go.
More than that, Bliss currently supports iOS 4.3 as its earliest version, so if you want to support older iOS devices then you might want to limit your choices to fonts that iOS 4 had. If you choose to use a newer font and want to share your skin then it might be a good idea to warn people that your skin only works on iOS 5 (or 6 or 7, depending on the font).
And finally, unlike regular CSS, Bliss doesn't support specifying a list of fonts with fallback, so you'll need to choose one font and stick with it.