I'm attempted to combine different Varieties of acer platinum,,Japanese maples mountain maples "green" and red Japanese maple.. not exactly what you're talking about but kinda different. If you wanted to combine different species it's definitely possible. Where I live in Ohio you see marlbury trees and Hackberry tree's fused at the base all the time naturally. They are both tuff tree's that have a suckering habit and because birds poop there's seeds out in the same siting you get two tree's grown very close together and when they get larger they fuse. I've seen countless examples of different types of tree's fused together so I would think its do able. And welcome to bonsai nut BTW. I noticed you only have a handful of messages.