For us, that's a boundary. Everyone is different ofc, but for me, the husband, kissing is a no-no.
Thinking about it from a removed stance, it can be looked at as crazy from those not in the lifestyle with a thought process along the lines of:
"Wait! So you will let a random male dump his nut deep inside your girl, but you have a problem with them kissing?"
I have no issue with anything other than that. I love to watch, moreso, I'm behind the camera so we have footage later to watch and fuck to. I've always preferred to watch our footage over anything else.