I was told in multiple instances that these complimentary upgrades were indeed subject to award space... However, the agents might have been wrong. In my experience not all agents know how to properly handle these upgrades (either the complimentary ones, or the ones with the 50% miles discount). Even when they figure out what to do, they need to be sent to a back-office team to have the ticket re-issued, which takes anything from 2 days to eternity (ticket wasn't reissued in a couple of instances).