How would Dallas react to Ash turning out to be a robot?

“I just run the ship. Anything that has to do with science division, Ash has the final word!!!”

Kidding, he’d probably side with Ripley and expel his artificial ass into the void of space as soon as the opportunity presented itself.
Think about it, even if Dallas had reservations about it he would still side with Ripley on this one, Ripley wouldn’t even let Dallas back on board with Kane possibly mortally wounded, and don’t forget, Ripley was in a semi relationship with Dallas, fucking at the very least, and she still wouldn’t let him back on.
He knew enough about her to know there would only be one acceptable course of action to take.

he'd snap that AI asshole into two

Interesting question. I think he'd be pretty annoyed that the company sent an android along, and it's been following those orders.

Wonder how Kane would have reacted.

He would confront Ash, bringing Ripley along, and after speaking his mind and listening to Ash’s simpering excuses he would lunge at the android.

A brawl would ensue, but as Ripley watched them fight she would see no blood, only jets of white android-juice, and she would hear laughter. Soon they would both be laughing, and slowly turn towards Ripley.

‘Surprise!’ says Dallas as he reveals himself to have been an android all along. He and Ash high five. Ripley tries to escape but Mother seals the door.

‘And there’s one more surprise’ Dallas and Ash say in unison, ‘Feel for a latex flap at the base of your neck, Ripley’

Ripley obeys and to her horror discovers said flap, and in a fit of bewilderment, curiosity, surprise and dread… yanks off all the skin covering her head… to reveal a buzzing android face with spinning goggle eyes. She facepalms.

The Alien sees all this drama through the window in the sealed door. His excited mini-mouth retracts like a flaccid penis as he realises there are no humans on this ship to impregnate or kill. Depressed, he launches himself out of the nearest airlock.

THE END.