Are Star Pact warlocks the minions of the Far Realms? Are they actively (and I mean knowingly) going out and doing the Bidding of the Far Realms to further its goals?
If not, then why would they be at odds with Psionics?
Further argument:
1) Psionics aren't trying to destroy the Far Realms, just keeping it from getting closer/further entrenched/whatnot. To put it another way, the Infernal Pact warlocks have pacts with devils trapped or otherwise "over a barrel" in Hell itself. The Infernal Warlock would not be at odds with someone who goes out preventing Hell from spilling over any further into the real world, or who seeks to defeat Asmodeus. Because the things the Infernal warlock is making pacts with are prisoners of the denizens of Hell, or those "over a barrel", so those in charge of Hell are not on the Infernal Warlock's side.
With this in mind, given the "ineffible" nature of the beings in the Far Realms or whatever the Warlock has made a pact with, they may not necessarily want to encroach on Reality.
2) The Warlock isn't necessarily making a pact with anything specific. At least, he doesn't have to. By simply Understanding the Knowledge of the Stars, by "Peering into the Far Realms", the mere sight and knowledge of what Man IS Not Meant To Know would give him that power. It'd be like being half-sane, stained by what he saw, but that part which is insane has gleaned certain Power by Understanding something that is unable to be Understood. A portion of his mind has been torn out and replaced with UnReality, and from this area come his power.
So he owes no allegiance to any entity.
3) If the Far Realms invades Reality and everything is made an Aberration, and Reality as We Know it is Rent Asunder for the Otherness, then the Warlock is probably going to die become an Aberration himself. Hey, he's got power while the Entities are all the way out there. Them being any closer doesn't mean he's any more powerful.