This is basically an invitation to start throwing around random guesswork, which I'm reluctant to do because I'll freely admit I don't know how the relationship works. All I'm saying is that a lot of this - the Hernandez signing in particular - doesn't make much sense if you take it at face value.
If you do take it at face value then we signed a Venezuelan international for an almost club record fee - a signing that was utterly out of step with every other signing our manager made in the eight years he was here. He was then frozen out the team, even behind Logan who had already fallen out of favour at that time, by the same manager who gave Stevie May 60+ appearances in the desperate hope of recouping something from a far smaller transfer fee. At best you could describe it as weird.
With all that said, the questions you've made here aren't that difficult to answer if we start plucking scenarios out of thin air. They might have loaned us Gallagher under the assumption that we'd play him in X% of games - or at the very least it might have been explained to McInnes that he should play him to avoid damaging our budding relationship with Atlanta. The Hernandez signing might have been part-funded by Atlanta with the ultimate aim of him moving there (maybe as some way to avoid rules/financial commitments of some kind), but with us having no obligation to play him in the time he was here. I personally think Cormack probably just hired Glass because he already knew him, but if we want a conspiracy theory it's possible that Glass, having an Atlanta affiliation and being close with Cormack, would be more conducive to future weird loans/transfers than a complete outsider would be - from the perspective of Glass he gets to kickstart a managerial career so it's a fair deal if he occasionally gets a Jon Gallagher foisted on him.
I don't believe a word of that, but the point is none of it is necessarily illogical. I personally thought Gallagher looked technically woeful in his time here and was mystified that he was consistently getting in the team ahead of people like Hedges and Wright, but that doesn't necessarily mean anything either.