I've used foam wads from meat trays for years. I got started doing it when I was loading .38 wadcutters with very light loads of bullseye. The foam wad pushed down onto the powder with a pencil eraser kept the powder from all laying along the bottom of the length of the case when the loaded round was horizontal, a circumstance which makes detonation, rather than progressive burn possible. Anyway, after firing a few hundred rounds of those, I noticed little foam discs all over the ground. they were intact with one side sort of stippled, but definitely not melted.
I have also put them into 45/70 cases loaded with black powder to protect the base of the bullet. They also survive the discharge. The side presented to the burning powder shows the same stippling as the .38 wads did but what comes out is bore size, so there can't be much, if any, material deposited inside the barrel.
I've heard that the foam wads shouldn't be used because of the residue they leave in your barrel. That sounds like good sense but hasn't proved to be factual in my experience. Perhaps there are foam formulae which do melt at the stresses and temperature times encountered during the barrel dwell of a discharge but if so, I've not had any of it in the wads I've used.
I don't use foam wads these days for anything other than the very light .38 special loads. I believe, though, that the stories about them melting and gunking things up are just passed along from person to person without anyone ever actually trying them out. It just sounds like it makes so much sense, you know? I tried them before I heard you shouldn't and they worked fine for what I wanted them for.
So, I don't know how valuable they would be in a cap and ball revolver situation but by all means, if you think they are what you want, try them out. They won't hurt a thing.