I'm a die-hard Reed/Sato shipper, but there have been a few stories where I've posed a "What if Hayes and Hoshi got involved?" I honestly think there was something in that first scene in "The Xindi" when Hoshi sits with the MACOs in the Mess Hall...
HOSHI: What do you think of our doctor, Sergeant? I imagine you don't run into many Denobulans in Duluth, Minnesota.
KEMPER: Actually, I'm stationed outside of Atlanta. No Denobulans, but we have our fair share of alien visitors. You must have gone pretty deep into our records. I haven't lived in Duluth since junior high school.
HOSHI: You may have left Duluth, but you've still got plenty of Duluth left in your inflections.
KEMPER: Excuse me?
HAYES: Ensign Sato's a linguist, Kemper. You give her enough time, she could probably tell you what street you grew up on.
It's one of the few scenes where Hayes isn't portrayed as such as hardass. I mean he's actually joining in when Hoshi teases Kemper about his inflections.
I always got the impression the Major may have had a soft spot for Hoshi, and maybe this might have been a reason that Malcolm disliked him so much. Hayes is perceptive enough that when Malcolm called her "a friend" that she might mean more than that.
(In my AU Switcheroo series, Hayes and Hoshi are involved with each other...at least until Malcolm comes on the scene. LOL!)