Whitecoatinvestor has a great post on whether it's smart to consolidate with DRB or not. I don't have a link, but if you google "whitecoatinvester DRB resident refinance" it should hopefully pop up.
DRB does allow (require) you to make $100 payments while you're still a resident. I think another company (SoFi?) doesn't require any payments while you're a resident.
For both of the above, you'd lose any hope of loan forgiveness via Federal programs, so if there's any chance you will take advantage of them (assuming they stick around--we should know more in late 2017 when the first batch of eligible PSLF applicants pop up) then I would NOT consolidate any federal loans.
I consolidated my private loans with DRB--I got a lower rate and it was fixed, vs a variable rate with the private loans I consolidated. Usually the variable rate is lower and the way to go if you plan to pay the loans off quickly, but with the offer I got, it only resulted in a $10/month savings in a best case scenario (interest rates staying at all-time low), so I just went with the fixed.
So right now I just pay the $100/month to DRB plus my IBR payment to FedLoan. Totally manageable. If I knew I wasn't going to go into a PSLF-eligible job and/or it had been eliminated by this point, I may have consolidated all my federal loans as well.
I'm still holding out hope that the next president or two will finally definitely do something to help borrowers that doesn't screw everyone else (like PSLF would for high earners/borrowers--it just foots the bill to taxpayers). It'd be nice to consolidate federal loans with a federal consolidation loan at current rates. This is the reason DRB and those other banks are making so much money--professionals with a lot of debt but the ability to pay it off see they can save a lot of money with these banks, which means the gov't loses out on that class of borrowers most likely to repay their loans.