Technically yes. I am no expert but I understand the best approach is to divert attack traffic to a sinkhole, i.e. handle attack traffic, not block it.
Depends on the DDOS method used. Stuff like the NTP abuse of a few years ago could be sinkholed without effecting any real users. HTTP DDOS has pretty low impact per node so most attackers use some form of amplification attack with other protocols.
The key word is "provable."