This is a fairly subjective question because there is no canonical answer that I can find in the Emerald City materials including the Player's Guide to Emerald City, Secrets of Emerald City, and Emerald City Knights. But here are a few possibilities.
Quite well, thank you
One way to look at the situation is that of mechanics. Mind Control gives you certain mechanical advantages. You should be able to use the powers you bought unless your opponent has explicit immunities to Mind Control or your power's descriptor. Paging through the character profiles, they don't have these immunities, so at the least, this is a Hero Point situation.
I can feel another presence...
If the player has a Mental sense, there's a decent chance that they'll notice that the target they're trying to control is already being controlled. This may open the situation up to the next option.
Although they should be human, their mind is alien...
The builds, as they stand, down't have Immunities to being mind controlled. However, as GM, you may decide that they should. As is generally the case, be wary of including enemies that a player's powers are impotent against because it can feel very adversarial. However, having this show up in the first encounter as an outright Immunity, and in later encounters as a penalty to the check, followed by full usage as the character figures out the trick due to the nanites, is good roleplaying. But award Hero Points for this in accordance to how much it mucks up the player. Someone whose entire schtick is mind-control will get more points than the person who has other options, and someone who never even tries probably shouldn't get anything.
Making them do something specific is hard... but I think I can jam the signal
Making a target do something specific generally requires three degrees of failure for Controlled, or at least two for Compelled. However, Countering just requires an opposed check. The player may find it easier to set a target free than to control them, although they may find to their chagrin that said target, once set to their right mind, is still criminal.
Weird... my technopathic powers are letting me insert instructions
Lastly, possibly somewhere outside of your original question, the intersection of descriptors, since some Stormers are being controlled via their nanotech, is that a power that does not offer Mind Control (say, Comprehend (Machines)) may be readily Stunted to allow for Mind Control. This is the power of descriptors.
