"4. Eligible Securities - Traders can buy any common stock, preferred stock, or ETF listed on NYSE, NASDAQ, or AMEX exchange that is quoted by our data vendor with a bid of $.25 or higher. Traders cannot trade pink sheet stocks, mutual funds, options, futures, or bonds."
It doensn't specifically prohibit OTCBB stocks. But it doesn't say they allow it either. The rules should be clearer. I also though that people in this game were trading OTCBB stocks.