yes you can. just look at the short interest, which itself does not give a full picture since any short position closed before the record date doesn't get reflected. But just the fact that there is any short interest at all indicates that it can be done.
1) those with international accounts can short anything.
2) MM's can short any time they want
3) even some American brokers (i.e. I think interactive brokers) let you short OTC stocks too.
is from a website that claims to track daily short selling of OTC stocks. If accurate, its data shows that EHRC does have someone (traders, MMs, who knows?) selling short almost every day for the past month.
Also, as Krom mentioned, the online broker Interactive Brokers does allow short selling of penny stocks. If you go to the link below and click on "Check Availability", you will see that they currently have 500,000 shares of ERHE available for shorting.