First, what you need to remember is that Humans are not the first species to use them for other purposes. The Predators used them too, as game. And they used them for the same reason that a corporation might. You have a self-replicating, fast replicating (given enough hosts), extremely hostile, and hard to kill "perfect" organism. No overhead, No need to breed and train them. They do that themselves. If there is one thing any corporation, real world or Alien universe, strives to achieve it is profits. Less overhead means a lot more profits.
Also, remember, Weyland-Yutani never really understood them. They seemed to think they could somehow domesticate them like you would a dog. That they would be able to bend the will of a hive to their whims. As we all know, thats futile. They have a genetic impetus to spread and kill. They are pure in that way. No thought of morality, no f*****g each over for a profit (thank you Ripley). Domestication will never work. Despite this, they still funded R&D programmes to try. They felt the money sunk into it in the beginning was worth it. That the eventual product would pay for itself eventually. And, due to the fact that their Xenomorphs were domesticated, there would be no need to worry too much about them when the company lands their colonists or whatever they plan to do. Just round any Xenomorphs up and either keep them or euthanise them.
Then there is the other factor: deniability. Xenomorphs are the perfect bio-weapon for such a task. A bio-weapon that any corporation could use and say that there must have been Xenomorphs on that planet or whatever. You said it yourself, it only takes one Facehugger. It would be so easy to deny everything. Yes, other corporations and governments can point the finger, but unless the Xenomorphs used are branded "property of Weyland-Yutani" it is feasable that either the planet had a dormant hive no one knew about, or a colonist was already infected, meaning no proof.