I'd say yes. At a conference-related event, you still represent your company on some level. (This of course assumes that the events happened as stated.)
As someone pointed out, this is still an allegation. If the allegation alone leads to firing, then another way to look at it is : the best way to have someone fired, is to make an allegation like that against them.
Also, since the developer is still representing your company at a conference. Accusing the developer of an assault is also a good way to tarnish the company's image.