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."