I just played the all time classic Aliens Colonial Marines game and I saw that the WY PMCs played a significant role in the plots development.
The study and breading of xenomorphs was done by WY and several atrocities were committed in the process. However the USCM was unaware of their little project and as such was taken by surprise. In an attempt to cover it up the WY is willing to sacrifice a few hundred marines to cover up the mess.
I believe that something similar could be done in cm to enrich the plot and give WY the feel of the evil company that it is, willing to sacrifice life for the sake of profit.
I have a few ideas as to how that can be done.
For example WY PMCs could be on the ground in order to contain the infestation of Xenos and eliminate the colonists to ensure the secrecy of the operation. However the destress signal sent by the colony will also be received by the USS Almayer which will in turn move in to investigate. As the marines become essentially witnesses the PMCs become hostile and this battle between the USCM, WY and Xenomorphs ensues.
In a similar fashion the same thing can happen to other maps with WY facilities where the PMCs attempt to rescue their personel and eliminate the marines as witnesses.