Are you carbing cold? If so, do you notice any difference in how long it takes to get the dry hop flavors?
Do you do anything to purge oxygen from the hop bags before you put them in?
And when you want to remove the dry hops, presumably you disconnect the gas, de-pressurize the keg, open the lid, retrieve the bag, replace the lid, reconnect the gas, and re-pressurize again. Any issues with loss of aromatics from blowing all that gas out?
I rack from primary to keg, drop in the filled hop bag, bring the temp down and apply gas all at the same time. You MAY get better dry hop infusion at room temp, but I'm killing three birds with one stone carbing/cold crashing/ dry hopping at once. Plus I'm sampling daily to know when to pull the bag. Depends on the beer, but I'm usually pulling the bag in 3-5 days.
You are right about disconnecting gas, relieving pressure, open lid...all correct. I think the loss of aromatics would be very minimal if any...none that I can detect. The gas volume in the headspace of a full keg is a small volume. As long as the flavor/aroma is infused in the beer, the CO2 off gassing bubbles (fizzing) brings the aroma to your nose in the glass when served.
I spray a muslin bag lightly with star san (just in case), add hops, tie off and drop in. Since the bags I use are like cheesecloth, there is no real reason to purge.
If one dry hops post fermentation, why is sanitation not an issue, or maybe it is? I've been dry hopping at "flame-out" (my brew rig is electric so I just turn off the element). I can see where aroma would be lost the way I have been doing it, but I'm concerned with sanitation. My dry hop pellets are contained in a stainless cylinder with a screw on cap. Would I just sanitize the cylinder and cap, insert my hops, then toss into the fermenter?
Yes, I suggest you do that preventive sanitation measure as described. I lightly spray my muslin bags with star san before adding in hops and dropping into keg. However, fermented beer has an advantage to fight off infection since bacteria is typically held at bay by the alcohol present in the beer at this point. We are always careful for sure, but fresh wort is way more susceptible to infection compared to fermented beer.
One area of concern is dry hopping fresh fruits in fermented beers for flavor infusions. Hops are typically ok, but fruits carry tons of crazy bacteria on their skins making them very suspect. But we are talking hops, not fruits...sorry to wander off topic.