Not necessarily. You can short whatever you like (depending on your broker/platform). The risk comes when you bet wrong and owe more than you hold on the account. If someone is shorting a stock that rockets upwards, it is possible to drain the account to a point where money is owed. Buying and holding just means you could lose it all, but not owe.
You don't want to short something you can't cover, but stocks fail in the OTC all the time. DRYS has been a great example of that historically. R/S then short into the ground like clockwork.
On the other side, what I'm seeing on USRM chart is a near term historic low in price. You'll see about 6 months ago that they were trading at next to nothing, but as of the last 3 months have added and are holding value. The pop to .17 was clearly artificial, but they'd REALLY have to throw the game to go much lower than this with the current interest in stem cell tech. That said, the company still needs to provide investors with knowledge that USRM is doing well on the business side and making money. Severe losses would be unacceptable, and it appears that focusing profit was their big goal in dropping RMAT pursuit for the time being.
They need to innovate, advance AND profit. No point in being cutting edge if you can't make a buck.