You can use whatever models you like to lead your army as long as you're clear about what counts as what, so if you want to use Space Marine models to represent your HQ choices, then go for it.
As for using actual Space Marine rules... yeah, not so much. The closest you could do would be to take a Grey Knight Hero with a Terminator Retinue as an HQ choice from Codex: Daemonhunters. But you'd still need a Guard HQ as well.
As for using actual Space Marine rules... yeah, not so much. The closest you could do would be to take a Grey Knight Hero with a Terminator Retinue as an HQ choice from Codex: Daemonhunters. But you'd still need a Guard HQ as well.
