Is it possible to have th BoS actually fight with me at Hoover Dam while siding with Yes Man? I have a good reputation with them and have completed Eyesight to the Blind already, so can I officially join with them by either ignoring or interacting with them in Wild Card: Side Bets.

No, you can't get them to fight with you. You can only ally them with the NCR. Then they'll fight alongside you if, and only if, you're fighting for the NCR.