Invalid how? what do you see ?
The target vc server no longer shows up as a virtual center system. When we attempted to re-deploy the VC CO, it said it did not find a VC target.
Upon further research, we found out the VC Admin deployed an earlier version of the agent, therefore the CO was invalid (as it was for version 8.7). Once we upgraded the agent to version 8.7, the CO was able to be re-deployed, and target is now vc enabled.
So, long story short, 8.7 supports Virtual Center 6.0 Update 2.