I don't think that's a limitation. Swype is based off the dictionary and words you input., I'm guessing you could try to input 345 and see if that ever comes up when you Swype. , I've gotten 3g on here where I don't have to manually type that in anymore and I can Swype it.
I've not had any success getting Swype to allow swyping of numbers. Like Duvi said, it's more for words, based upon a dictionary to autocorrect and select. With numbers, times, etc, there's no way to confirm accuracy.