Market, Not app?
I had this same issue last week, but I flashed another rom and Droid Overclock was in the market. I never thought about this until now, but my guess is that the market isn't recognizing Rom banner that you are using.
You people that are having issues with Droid Overclock, check to see if your rom has "Verizon Wireless" in the notification drop down shade. Some developers use their rom name in the banner instead.
This sounds funny, I know, but I used to have similar market issues with my OG Droid. Sometimes, when I would load a rom that didn't have "Verizon Wireless" in the notification banner, certain apps wouldn't appear, even though I paid for them.
Hope this helps.