Its for sure a pointless question.....although I cannot speak for others, at least some of us (and maybe a lot more than some) are pretty much sex animals, swapping raw loads with many dudes, letting it all fly and losing control and count. Even those of us who respect a dude's right to an honest answer may not know if they are shooting charged cum; there's no shortage of dudes who think they are "clean" until they spend hours on the thrown dealing with the Fuk flu.
Personally speaking, if it mattered I would just ask a dude his status, which is direct and isn't rude (although given how I behave I personally am nit offended or surprised when guys ask me if I'm clean)