Are you going to be using an automatic controller or a manual twiddley knob jobby?
I ask because if you connect the two speed signal wires (the ones that arent red or black) it could end up in a mess that would confuse an auto unit, or anything else used to display their speed.
EDIT:
Didnt write quick enough to see your post just above this, using that controller and the splitter should work fine, as long as you use matching fans in the pair.
PK!