My understanding from people who have done it is that:

-- Yes, you can outsource most of the payroll-related headaches to someone like ADP but

-- There are still a lot of other state by state details that can't just be handed off to a third party and told "Make it so." It's not a particularly big deal for a larger company, but it can be a fair bit of overhead for a small employer adding a new remote employee in a state with lots of paperwork.