Grey area. 'They can use this slot to install any one armor upgrade'.
I would say no. For two reasons. 1) It doesn't make much sense, I might allow it if they used the rules for adapting armor to new and unique physiologies before using it for two slots, but that leads into 2) This is really only a problem at very low levels. There's no reason not to get slightly better armor, or weaker armor with more upgrade slots if you really want a force field at level 1 or 2.
Combining slots in that way is specifically addressed for Integrated Weapons, but not for other multi-slot upgrades.
"An integrated weapon can be wielded normally or installed in an armor upgrade slot. When properly installed, the weapon is considered to be wielded without needing to assign a number of hands to wield it. An integrated weapon requires the listed number of armor slots for proper installation. An android or any other creature with the upgrade slot racial ability cannot combine its racial upgrade slot with armor upgrade slots to install an integrated weapon. Installing, removing, or replacing an integrated weapon in a suit of armor takes 10 minutes, as if it were an armor upgrade."
Even in that case, racial slots are addressed, but exocortex mechanics are not.
Forgot about the 4 slot integrated weapons, those would be a relevant problem for much of the game.
Still, from that rule, I'd definitely say the answer is no.