It can be done but they will be two different memberships. You will not be able to combine the points for a single night without the transfer.
If you had to wait a reservation and had to use points from both contracts, you would have to transfer before the wait list even came through.
If they are the same resort, its easier since you can book whole nights from each and then link the reservations, but it does take a little bit of work. We had two UY's at one point, and IMO, it is more trouble than its worth, unless you have a specific need to own two.
Good luck!