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Thanks for the replies everybody.. Good to know that it's possible.
I have the ER-X right now (along with the other equipment).. I didn't realize a switch would have been better in this case, but I chose the ER-X primarly for size and cost. I initially was going to have an ER-X in buliding 2 with one port assigned to the Satellite 1 VLAN, and another port assigned to the Satellit 2 VLAN, and reuse wireless access points that they already have, but I really like the managment features of UniFi AC AP and it would simplify there network configuration overall.
I'll need to capture screenshots of how I tried to configure it, and the errors I've gotten, but this is what I'm trying to do.