I would say "Go check it out", the dirt there will let you know if it is too soon. Weir loop was one of my favorite rides when I lived in o.c., more than once I tried to be the first out there after the rain. (assuming your starting from hidden canyon? end) the uphill section of trail that leads to the loop will cake your tires if it is too wet. I'm sure though that the P.C. answer is, if oaks is closed, Weir is also.
Rode Weir this morning, it was drier than Oaks (not as tacky) but open. No mud anywhere. The dirt in the main part of Oaks was incredible.