Agreed. While I think there are situations where having any sort of disability would limit the utility of an individual, that by no means precludes them from being quite valuable in the same role with different circumstances. Perhaps a solution to dogfighting with a deaf FC could be people using text comm macros that have supported wildcards built in (e.g. LCtrl+Shift+Z == "Committed on <current target>" -- in a CIC role this could also be tied to a blue force tracker like system that automatically flags that target as having been called giving it wide utility).
Any direct dogfighting leadership roles (Wing/Squad commanders) might prove difficult due to the heavy use voice comms usually and the issues you've noted with STT. Standard fighter roles however wouldn't be difficult with enough of the aforementioned text macros. An option could be made where text messages from certain individuals cause and audible cue and that might help significantly towards getting input noticed.
I actually think that the larger the group being commanded the less importance hearing would be if only because you are generally receiving input from relatively few directions and they are all known. As somebody else said, commanding in the BF series is a great example of that type of gameplay that is pretty agnostic as it pertains to hearing ability.
In the end though, we are still too early to be sure one way or the other. I actually think the launch of AC 2.0 w/ boarding and combat from FPS will be the first indicator of where everybody's talents are going to lie when it comes to combat.
