Don't you think if an altered strain was virulent and got out, they would be found out in this scheme you are concocting? They patented their crime...not logical
And investors are looking to make a return on their investment (research funding). If you create a drug, you don't want it to be given away for free. That's a very expensive process.
On the other hand, there was no market for any ebola vaccine before this tragedy. So it's really not some coincidence that it's been developed in the wake of the outbreak as the need for it has skyrocketed. Less of a conspiracy and more just business to be honest.
Pharmaceutical companies don't even invest in antibiotics anymore because the market for them is low at the moment. Too many are already on the market.
This is not even unprecedented. Plagues happen, and will continue to happen everywhere on Earth. On the grand scale of things, this outbreak isn't even close to the worst viral outbreak the world has seen. Google Spanish Flu for a starter.