Dulfy.net has a nice guide, as usual, to the new stuff in 1.5
including the new Cybertech L400 droid component schematics
that can now be purchased with Daily Commendations. All require Grade 8 purple and blue crafting components, btw. Any, my point here is that all of those tasty new parts all have Aim as their primary stat. There are basically 2 sets for a DPS companion and 2 sets for a Tank companion, depending on how you want to kit out your droid.
But, if you're getting yourself an HK-51 and you do what needs to be done to get Enriched Durasteel, Molecular Stabilizers and Synthetic Energy Matrices (and you know a Cybertech who gets the several hundred daily comms to buy just one set of the schematics), then you may want to go Aim on the other pieces of gear you put on HK as well.
I guess there is a bit of a vanity issue here as well. Do you want HK to use a Sniper Rifle or a Blaster Rifle? Nice to know (as the previous poster tells) that HK can use either, and that the Cunning on the Sniper Rifle counts as much as the Aim on the Blaster. Too bad he can't use assault cannons or dual-wield pistols....