This has been mentioned in 2016 and no fix came. I hope a fix comes soon as it would make them at least fun in TW if no where else. From the code listed on swgoh.gg and the description of the leader ability, it really does say that the ally (geo or not) is the one who applies the DOT, therefore it should trigger the TM gain if a Geo ally lands a crit and therefore a DOT.