Oh! Oh. I thought you were referring to a non-NPC character for a moment. Whether I give you permission to use Zack depends on what you plan to do with him. Could you run a scene by me real quick just describing the major actions you plan to have him take? (PMs, if you can.)
...In Fallout? No. Considering his habit of only posting when he feels like it, I think it would be better if we just kept posting while we wait for him to confirm he wants to RP with us before dedicating time to waiting.