Sure you can. PIPE financiers practically always do that. CEOs who sign on the bottom line know it too. That's why Sedona insisted on a "no shorting" clause in its PIPE agreement. But Rhino ignored that and shorted anyway, which is why they got smacked.
This is a gray area. Toxic financiers have been doing it for a long while, and regulators haven't objected. Note that the article refers to "improper shorting" rather than "illegal shorting".