Hayes was made into too much of a by the book guy, even going so far as blindly following the chain of command no matter what - someone should've reminded him that that defense failed at Nuremberg.
Culp has said that originally he was offered 10 episodes and then it got whittled down -the final # is 5. Per Memory Alpha -
"The Xindi" - intro stuff, mainly, an inkling of the conflict with Reed.
"The Shipment" - he mainly just guards Graylick and doesn't have a lot to do.
"Harbinger" - fight with Reed.
"Hatchery" - just following orders.
"Countdown" - won't spoil it for those who haven't seen it.
But he didn't get a helluva lot to do, which is unfortunate, as a character in open conflict with another senior character would have been far better drama if it had been sustained longer. Instead, the arc is incredibly short. Hayes could have been seen more, and you can see instances where Culp was probably supposed to be there, but maybe TPTB wanted Keating to have more lines/air time, so it was Reed leading MACOs into battle, which kinda doesn't make much sense. Was Hayes on vacation? Injured? In the Brig? A throwaway line, here or there, offering a smidgen of exposition, would've been nice.
I would've liked to have seen him in Impulse
, instead of Hawkins, for example.