If counterfeit Tether has been used to prop up the market the losses of the comparatively few people who actually hold Tether will be a drop in the ocean compared to the affect on BTC price. The bitcoin price is a function of demand, if Tether tuns out to be a scam, and has been used to artificially inflate that demand, then the price can only go down. There is also the problem that if Tether collapses, there will be a run on all exchanges that accept Tether, particularly Bitfinex, and the resulting panic will send BTC through the floor.