That's pretty much the way they work. He doesn't stifle her natural behaviour and she accepts him for the way he is :D I suspect Illyria and Dawn will turn into sparring buddies at some point and that when Dawn does her globe-trot thing, she'll take Illyria along just to shut Spike up :D

Also, had a thought for a scene at some point after Dawn gets herself immortalified (which I now have a number of possible options to follow-up) - she's sitting on the lawn with Spike, just after sundown and she admits to him she did very silly, painful trials like he did for his soul and he's just gaping at her and asking why and she shrugs and says "because he keeps losing people. I didn't wanna be another one". Boggled by how much she cares, Spike wanders off and even before he's out of sight, Dawn murmurs "and how much of that did you overhear?" a moment before arms slide around her waist out of thin air ;)

*wibbles* Poor VK! Having to eat someone that close has to be bad.