It all depends on the slip joint.
Some, like the Buck 301's and 303's, have springs that are not that strong. If the leather on the glove is not that thick, sometimes you can get enough of a nail impression to open the knife. Others, like a single blade barlow or daddy barlow or sodbuster, can be pinched open with gloves on. SAK's and most of the rest you have to take a glove off. In this respect, I've found that friction folders have an advantage in that you can sometimes knock the heel of the blade against your other gloved hand and the blade will pop out a bit. Opinels have the handles shaped for this.
Of course, if I'm going to be out in freezing weather and I know I may need a knife, a small fixed blade is a great thing to have. I do believe that this is why our knife loving cousins in Scandinavia, have such a love of the puuko type of knife and don't even deal with folders that much.
As far as cleaning after dressing game, again if depends on the knife. A two blade Texas jack or sodbuster is going to be a heck of a lot easier to clean out than a SAK like a tinker. It can be done, and I've done it. But mostly it was an experiment in nostalgic minimalism. All the old guys I knew growing up all carried a sheath knife for game. They all had a pocket knife of some kind that was their 'everything' knife, and the sheath knife was reserved exclusively for game. They ranged from the Little Finn style of knives made by Case, Kabar, Western, and a few others, to the German made stag handle Edge Brand knives that had those great one piece stag handles in the old country style. I never saw a folding knife used for game processing until Buck came out with the folding hunter. I have to hand it to them, a folder is not a great knife for dressing game, but they created a whole new knife market that they ruled for many years.
Carl.