I really don't believe it is corrosive, and eats bearings. If anything, it may contribute to early bearing failure, due to washing away all the oil. WD-40 displaces moisture, this is true. But it also displaces oil.
And just because Traxxas recommends it, doesn't mean it's the right way. That is a company that I wouldn't trust to give the whole answer, or the right answer.(Just ask them how much oil is in their fuel)