I believe this is, in part, exactly how Intellectual Ventures operates.

Even if they don't have a patent on something, they can use interference to get some cross-licensing settlement going.

You'd have to show that you were engaged actively and continuously in working on the invention to maintain the ability to sue, and ultimately you'd have to show that you were entitled to receive the same patent that the other inventor filed for (in other words, that you actually invented the same thing). There is also the fact that it's often years from when a patent issues to when it becomes cash-flow-positive.

So, at the end of the day, if you're paying all of these scientists to invent, you'd do better to just file for patents on what they're inventing and license those out.