If you think employing open-source maintainers gives a company "control" over a project, you haven't met many maintainers.
In any case, IBM is very respectful of the health of the open source projects on which it depends. While the vestiges of Red Hat may become less and less attractive as a place for a maintainer to work over time, I do not expect IBM to exert any control over any of these projects in any meaningful way any more than it has over the areas that its current employees maintain. Look at SCSI in the kernel, or even RCU, both maintained by IBMers (two examples among many).
(I worked at IBM in its Linux Technology Center for over a decade)
In any case, IBM is very respectful of the health of the open source projects on which it depends. While the vestiges of Red Hat may become less and less attractive as a place for a maintainer to work over time, I do not expect IBM to exert any control over any of these projects in any meaningful way any more than it has over the areas that its current employees maintain. Look at SCSI in the kernel, or even RCU, both maintained by IBMers (two examples among many).
(I worked at IBM in its Linux Technology Center for over a decade)