I noticed that too (he's also not mentioned as a guest star in the opening listing over Act I, even though he's the main antagonist). But I'm not in Phase II's or Vic's shoes, so I'm sort of inclined to give it a pass.
I do think Vic's performance in the episode is very strong.
Ah... I know nothing about filmmaking, but I watch a lot of TV. The 'guest star' is often cast as the main antagonist in procedurals. Perhaps that's not true in other TV programs, but this would be normal in a procedural. He isn't the 'guest extra' or the 'guest supporting actor' or the 'guest cameo' he's the 'guest star.'