I really don't recall which, it was a while back. Don't think it was the fix-a-flat stuff.
The problem as I recall is the stuff is water based and over time will cause rust on the inside. Since on some ATV's the tires are on there for years and years, when you do take it off you then see the mess.
If slime isn't water based then you should be ok. Also not sure if they recommend a different schrader valve. But since I put mudlites on my KQ I haven't got a flat. 6 ply tire if I recall.