To my experience HM x VT = round tail, a few deltas, and a bunch of VT. But then again local breeders in my area loves to experiment. So the HM's are not pure.
I agree with 1fish2fish, in 2 - 3 years you'll need to get new breeders. If possible, get breeders of the same tail type. If you want to experiment, do it to colors not tail type.