I do it routinely, using a small outlet expander (expanding 1 outlet into 3 outlets). The only issue I occasionally worry about is that whichever one of your carboys has the thermocouple attached is the one that gets to decide whether BOTH Fermwraps are on or off.
The scientist in me says that it is incorrect to assume that the fermentability of the wort in both carboys is exactly equal ("exactly" being the operative word), since the volumes came from different parts of the kettle. Even the yeast pitch into the two carboys HAS to be different, even if it comes from the same starter flask, because even IT stratifies a bit in the time it takes to get from the stir plate to the carboy mouth. I always allow my wort to settle down for 30-45 minutes after I stop the chill/whirlpool cycle, so I'm sure more than just hops and trub are settling down; I'm surely getting some sort of stratification going on as well.
That said, I still do it, and I cannot discern the differences between the two volumes. I maintain their separability all the way to the keg, and can't tell the difference between the kegs. I guess if I were REALLY worried about it, I could blend the two volumes together before I kegged them, but that would expose the now-finished beer to oxidation, and THAT worries me even more!!
I need a homebrew... I'm worrying too much...
Indecision... may or may not be my problem... I'm not sure
Primary 1 - Koelsch
Primary 2 - Maerzen
Coming Soon: An upgraded Blichmann 20-gallon, Kal-inspired, BCS-controlled, RIMS pico-brewery (by mid-Summer 2013, after the NHC, I swear!!)