"Ork" is used by Tolkien (it was his preferred spelling, apparently). In
The Adventures of Tom Bombadil, he wrote this:
I'll call the orks on you: that'll send you running!
And while that was published in JRRT's lifetime, I'm pretty sure that posthumously published stuff has used
ork and
orkish since. I suspect that the Tolkien estate is quite a big hitter when it comes to IP protection, and it certainly has form for taking on games companies. I'm not any sort of expert on this, but I imagine that the Tolkien estate might be displeased (or even forced to act) if a company were to try to claim "ork" as its trademarked alternative for "orc".
Also,
orke is attested in English since the seventeenth century, according to the OED, and there's an
ork in Tyrolese folklore.