Utter nonsense. Plame was recalled from her last post as a covert agent in Russia in 1997, on the assumption that her covert status had been compromised by Aldrich Ames. From that point forward, the CIA operated on the assumption that her covert status had been compromised, i.e. that anyone who really mattered knew she was a CIA operative. Her covert career was absolutely over at that point. If any other real covert agents had been using the Brewster-Jennings front, they would have been presumed compromised at the same time (since Plame had already used it at the time she was presumed compromised). The fact that she — a compromised former covert agent — listed herself as an employee of Brewster-Jennings in 1999 in connection with her $1000 donation to Al Gore’s campaign, obviously knowing that such affiliations become a matter of public record, proves that Brewster-Jennings was no longer a cover for any covert agents at that time.
Not every front company the CIA uses is cover for covert agents; many are just for convenience. Truly covert agents are generally planted in REAL companies or government offices (of both US and foreign governments). When CIA-created front companies are used by covert agents, the compromising of one agent would necessitate the immediate dismantling of the company, or at least immediate cessation of its use as any kind of cover.
Do you have a source for that, outside of speculation by people who want this to go away?