Magic Staff included in a weapon

[Bonzai]

I think that there are rules for combining magic items in the Magic Item Compendium. Normally it's for two items covering the same slot, but it's more or less the same thing here. If memory serves it costs 50% more than the individual item would on it's own (the item effect that you are adding on top of the existing magic item). Still, as the others have said, it's up to the DM in the end.

I would allow it just fine.