If I have a dessi with me on a raid, I ussually shoo him off a few K so I can pirate.
Now as far as helping out when the flood arrives, it is free to open up. To have a Dessi close by (a couple K) isn't against the rules, only if it attacks. I would also think it is deffinatly not OORP for a trader to get a cold sweat with one sitting silently nearby.
When with other raiders in Varyag, I ussually sit about 7k out from the ambush just to be on the safe side.