Can Ghillie place his companion on the board AFTER he moves? For example, I have the "Trust Your Gut" encounter which allows me to move 3 spaces after my attack. Can I do the attack, move, and then place the companion (assuming I roll the companion together with the attack dice)
Can't see any reason why not.
Ghillie or any other Gearloc always move before rolling and resolving dice so I think your question is more if you can wait until the attack is over before deploying a companion.
Since the dice you roll can be resolved in any order, you could for instance
choose to resolve the attack first before resolving any companion die. In this case you would be able to then move Ghillie 3 spaces before deploying a companion.
Technically, if you resolve the companion die prior to attacking it would have to be placed right away as all Companions are Instants.