Not in my experience. I was there in July, it was all WOC from park open until 11:30 AM or so, then half GRR half WOC for the remainder of the day until WOC FP were all gone.
The time they switch machines from WOC to GRR may be different day-to-day depending on attendance levels and demand. Today (Sept. 17) was a cool, overcast morning (what local meteorologists call the "marine layer") with the sun not breaking through until nearly 2pm. When we walked past GRR at 1pm, they were not yet distributing FPs for Grizzly River Run--and with a standby wait time of 5 minutes, they didn't need to. The cool weather probably dissuaded some guests from riding, keeping the wait time low.
As we walked back past GRR at 2pm--heading over to DL--we noticed the FP machines were finally on for GRR. Standby was up to 15 minutes and the sun was finally making an appearance.
First thing in the morning all the GRR FP machines are distributing WoC Show tickets. Later it changes to GRR FP + Woc Show Tickets, lastly if crowds warrant and all WoC ticket are distributed it will be all GRR FPs.