RECs for project supplied by campus central utility plant?

Sure, I don't see why not.

I could not find any definitive guidance on this, but this article from EPA states "CHP emissions are accounted for as Scope 1, or direct, emissions when the CHP facility is located within the facility boundary. At the same time, the CHP will displace amount of grid electricity consumed by the facility. The CHP could also be accounted for in a facility's Scope 2 emissions when the CHP provides energy from outside the facility boundary." For the purposes of this credit, it might depend on whether you model the campus plant as supplying purchased energy to the project, or as a virtual on-site plant (Option 1, Path 2: Full DES Performance Accounting). If you model the electricity, steam, and chilled water supplied by the plant as purchased energy, then the electricity supplied by the plant should be considered Scope 2 and should be eligible to be offset by RECs. If you model a virtual on-site plant, then the only energy source you would have in your proposed building model will be the input fuel to the cogen plant (assuming the central plant supplies 100% of the building's electricity), and this would have to be offset by carbon offsets.