Sure, but why would you advertise to those people? There are many very talented people in parts of the world that aren't the premier market for their skills that accept much lower salaries for their skills, or are employed in other industries altogether. I wouldn't be surprised if the number of people that match that criteria and have security research experience is much higher than the number of people in Silicon Valley and the other 5-10 leading tech markets that have the requisite security experience.
The world is a big place, and I think exploring security is fairly attractive to the weekend warrior programmer that might find other work hard to come by.
Fixed price anything (job, bounty) means very different things to different people.