Yes you can call MS and make your ADRs. However, if you want to make the first call of the day, you should call Disney Dine since they open at 7am and MS opens at 9am. Also, if applicable to you, MS offers a toll free number.
Otherwise, I believe it's the same. I've done both. I didn't see a difference between them. But if you feel the need to call at 7am, MS is not your best option.