I have a bougainvillea book...that shows grafted bougainvilleas on one trunk. Having their bracts complimenting yet contrasting can be amazing to see, Since their care would be the same...I would not see an issue with this combination pot. Though the roots would eventually tangle so you might not be able to later take and separate them. But I see no issue with them potted in the same container. Same care goes into each variety. Roots growing from the bottom of the pot...you may wish to have it on something so it doesn't root into the ground where it sits. That is suggested in the book I have.