Other way round, IBM are hoping that a lot of their customers who aren't already big Red Hat customers can be converted to using RHEL and (especially) Openshift. They already have all the sales and delivery relationships in place that they need to do really big (like 100 million to billion dollar big) deals, much bigger then anything Red Hat has been able to sell on their own. They also have relationships to sell RHEL/Openshift to IBM customers that RH struggled to get through the door of. So if they can get big growth in the number and size of Red Hat deals by selling to their existing customers then they can grow RH massively and of course all growth in Red Hat deals is growth in IBMs profits.
And if they can sell some of them RHEL on POWER9 they will be very happy to take that money as well :)