Winger Hylton, who scored a hat-trick against the Millers last season, has penned a two-year deal after leaving Aldershot.
Milsom, a versatile player who can play in defence or midfield, has spent the last two years with Aberdeen and has signed a six-month contract.
"I am absolutely delighted to eventually be in the position to have got Danny and Rob at the Millers," boss Steve Evans told the club's official website.
"It has taken a little longer to get both signatures and until we had both I was fearful they would have been snatched elsewhere.
"Both lads have got great ability and will greatly enhance what we have in the squad."