Not my thing nor have anyone I know who does it. I don't doubt it exists, though in my 20+ year run I have only had two guys comment on this. One session many many many years ago when I was renting from the Nutcracker Suite in NYC the guy complained bitterly that there was not "enough cum" on my boots from other slaves for him to clean. (Spoiler, there isn't any. I clean my boots for, you know, hygiene.) I have a local here who calls every so often to ask about "my supply" of client cum.

I spend an excessive amount of time trying to keep everything clean and avoid all possible ways of cross contamination. I think I will pass on cups of frozen jizz next to my ice cream. I don't feel it is all that healthy in reality.