He was quite an up-and-comer back then. Annapolis, Vietnam, and Secretary of the Navy. The American Spectator did review his novels in 1981 and 1984. The prospect of a writer who was both a veteran and at the time a conservative must have been appealing to them. I seem to remember something by him in one of their issues, maybe Christmas book recommendations, though perhaps I'm wrong: it could have been John Lehman. Unfortunately, the Spectator's old articles aren't online and most libraries only keep a few years issues on hand. Maybe Lexis/Nexis has more.
Webb's book Born Fighting did get a very good review in National Review, and he had an article published in the Weekly Standard. If they want to attack him now, fine. He switched sides, not them. But Tyrrell's account looks like a cheap shot. Tyrrell wouldn't have brought up Webb's past conduct if Webb hadn't switched parties, so it would probably have been better to have left it out. As it is, it looks like a kiss-and-tell David Brock move on Tyrrell's part. George Will says pretty much the same thing as Tyrrell does but doesn't claim to have known it all along.
As for your opinion that the article is a cheap shot, well, this is Bob Tyrrell, whose magazine regularly had the "Enemies List," one of my favorite regular features along with "Current Wisdom." And TAS did print the troopergate stories which led to the Paula Jones lawsuit, which in turn led to so much aggravation and misery for Slick. Perhaps Tyrrell does throw the low blow sometimes, but at least he always fights.