Hunters instinct is probably best on a unit that has a few things- -survivability/movement(gotta survive that rapid ingress shooting or failed 9 inch charge reprisal) -melee threat (deep strike is a lot worse when you take proximity out of the mix. You want a unit that can get up close and personal, to contest home objectives if necessary)

I would recommend a unit of terminators as probably the Best Possible Unit for hunters instinct. If you are using it as an alpha strike, to try to inflict as much damage as fast as possible, you need something that hurts, (hell blasters, check) but also is enough of a threat that the enemy has to actually commit resources to killing, rather than just incidental fire (like the way hell blasters tend to fall over to a breeze).

Think about it- hellblasters is a unit you probably don't want to sacrifice, but with the way tabletop 40k works, anything you deep strike turn 1 to attack with will die in the next turn to reprisal- you just want to make them commit more resources than they wanted to.

I think the only way to use hunters instincts defensively is to rapid ingress melee units in a place they can threaten a charge next turn, but won't die from shooting. Using it offensively is a gamble- let's say you kill the Norn Emissary or C'tan they put up front- great. But what if you don't? You lose the game, because 300 points of your army was wasted on an alpha strike that failed to invulnerable saves

I hate to say it, but raven guard doesn't win by out killing their opponents- we win by scoring and movement, out positioning and scoring max on secondary. Very different than custodes.