I’m designing a board that will carry 10GBase-T signals and requires 100 Ohm differential impedance. Can the standard DKRed stackup support this?
The differential impedance of a trace pair is as much (or more so) a function of the layout one designs as it is of the board material/stackup itself.
At this time the “standard” DKRed stackup is the only one offered, consisting of 1oz copper on both sides of 1/16" thick FR4. This offers very little flexibility in terms of signal routing while maintaining signal integrity suitable for 10G applications. So while perhaps not impossible per se, most such applications will be better served by a service offering 4+ layer stackups. At GHz frequencies, isotropic substrates are often a good idea also.
Bogatin’s Signal Integrity Simplified is a suggested resource for guidance on relevant matters.