What I see from this picture are 4 identical damage values. And during my testing, I was only getting identical values from the spark (same value every time). The DoTs were random with every single tick. So my guess is those are the 4 sparks from 4 different bullets. (or you got VERY VERY VERY lucky with RNG)
And there is nothing in the picture that can inform me that those are indeed DoT ticks and not sparks… 
Evidence, but not CONCLUSIVE evidence.
While the fact that the spark itself will appear in Vacuum or that it can crit with Tombstone was never put in question, I can’t accept this picture as PROOF that DoTs from Hot lead will proc in a Vacuum, sorry.
I know I sound harsh, but i’m trying to steer this away from confirmation bias as much as possible, So in essence, i’m trying as hard as I can to DISPROVE your claim. When I have failed, we’ll know it’s the truth. That’s the core of any scientific experimentation worth a damn.
I’d really really like to see a video of a burn DoT in Action in a Vacuum.
Something that CLEARLY and unequivocally isn’t damage from another source.
And to anyone who wish to help, please pick another gun besides the Luck Canon or the Omni-canon, as I have not run any tests on the moneyshot or splash’s effect on Hot lead’s damage. A careful Cartesian approach requires that we remove all non-essential variables. (it will also make the “if they don’t die” part more likely to happen
)
Please understand that i’m not trying to be dismissive of your efforts, I just want to do this properly, with a methodology that can’t be put into question.
One thing at a time: When we have proof that DoT from Hot lead can proc in a vacuum, we’ll move to seeing if it can crit. Right now, no tombstone, no nothing… just (conclusive) evidence of Hot lead procing a DoT in a Vacuum.