Yeah, they've always been able to possess just about anyone. It's just some bloodlines/hosts are more suitable for long term possession than others. And with all of the angels having fallen to earth, and only so many hosts available, it's no surprise that they're desperate to get any kind of suitable body they can by any means necessary.
That said, if this is the same Ezekiel who was a prophet that God rose from a human to divinity, and especially since Castiel not only knows of him but knows him to be one of the "good guys," I'm leaning towards him being, you know, one of the good guys. Especially since we've seen so very few angels who were. Having yet another
douchebag angel would just be boring and repetitive at this point.