I really should give the creature its proper name, which is "Coeurl".
The Coeurl is the Coeurl, and Displacer Beasts are Displacer Beasts. Gygax and company were shameless but rarely comprehensive unless it really was from a mythological source.
Many of the creatures that are distinctive to D&D would wreck a typical Traveller group, if only because a fair number of them are psionic and calibrated for powerful D&D encounters. Turning the tropes around could be fun, though.
Illithids, but as so far off the Human norm that they exhaust themselves using psionics on Terran forms (per the surcharge first seen in CT) and don't have a close enough biological compatibility to be able to eat the brains of anything but their own native life. Terrifying but harmless.
Githyanki and Githzerai. A race of natural Jaunters, locked in an internal war that others only get in the way of. Both sides are broadly honorable about it and try not to involve outsiders, but each also believes the other side is honorless, so they also snoop a lot to make sure. To the Traveller cognoscenti, the results will feel a lot like another skirmish in Grandfather's ongoing war, but is nothing of the sort.
I think Beholders would be a bit too blatant, but could be used much like the one behind the scenes in Waterdeep (no that's not a spoiler; he was on the cover of a 2nd edition book 30 years ago), similar to the Hutts of Star Wars.