I completely agree Jamie. It is hard to say what will happen. The joeys from that pairing would be possible hets since there is white tip in the line. It may also be possible that they could produce a white tip joey. It may not be likely to happen, but it definitely wouldn't be impossible.
The white tip genes are funny things. Sometimes white tips will appear out of sugar gliders with no history of white tips for several documented generations; other times a pair of sugar gliders with white tips will not produce a white tip joey. Of coarse there is always the middle ground, which is why all of this is so confusing.
There is definitely more than one gene responsible for producing a white tip. However, the more that white tip breeders have worked with the genes, the better they are getting at reproducing it.
I just brought home Jordon, a white tip female that has over 2 inches of white at the end of her tail.
She herself is a third generation white tip! So there is some progress being made.