all this is definitely stuff i've been thinking of for some time, but i have an additional element to throw into the mix: if dmitri is a spectral, whether or not he was in the activity club before, left it by choice, whatever, wouldn't he give off spectral energy that max and co. would be able to see?
throughout the comic, it shows up when spectrals use their tools/powers as mediums and/or in emotional situations. you could argue that dmitri's Effortlessly Calm And Chill demeanor means he's got a lock on it, but with that stunt he pulled in the hitball arc i postulate that there has to be something else going on. going off this (and a bit of wishful thinking) i'd say its more than likely that isaac's aforementioned Bad Thing happened to dmitri, and
or maybe its just so our/max's attention is focused elsewhere and im reading too much into it as per usze