I find these ideas a bit cheesy, to be honest. You're basing this on an assumption that a) the human race needs protection from the Predators, and b) that a corporation like Weyland-Yutani would be remotely interested in doing something philanthropic like taking on the protection of the human race, neither of which I believe to be plausible.
First of all, if Yutani (and later WY) knows everything from the previous four predator encounters (P1, P2, AVP, AVP-R), they'd also know that they only come here periodically for sport, and are far from being interested in anything remotely like global domination. In fact, pissing them off by collecting their weapons and reverse-engineering their technology is perhaps the only thing which would compel the predators to see earth as a threat worth eliminating.
As for the second point, I don't believe WY is interested in anything other than increasing its profit margin and market share. As for how the alien would achieve this, and why the bio-weapons division would be interested, you only have to think of what Wren says in A-R about new vaccines etc. They see the alien as a source of technological, and therefore monetary advancement, just like the predator's technology. You seem to be assuming that WY want to aliens to use as a weapon as-is, which is unlikely in the extreme. Also, why would they want to use the aliens to ward of predators when the two encounters between the species have showed that the predators would be more than able to handle them given proper preparation.
As for military applications, we have very little idea of the political climate in the Aliens era, but some drafts of Alien 3 hinted at a coldwar-like rivalry between the USCMC and another extra-terrestrial authority. Even without any such prevailing conflict, as an arms manufacturer WY is not interested so much in the use of its weapons as their sale, relying on the perception of a threat and the superiority of their technology to shift their product, whatever the reality of the situation might be.