It may not have been intended like this, but an 'experienced senior engineer' can also be a 'freelancer/contractor'. The post doesn't make it sound like that.
You want someone to be part of a 'team' - that'll totally be up to how you interact with someone, not their tax/corp status. If you want to be paying someone senior to help on multiple projects, advise on broader topics, etc., by all means get that. But if the person doesn't want to be in a W2 relationship with you, do you pass them over because of that?