Didn't they make their first apperance in Imperium, along with proto-hivers - making them pre-date Traveller itself?
Vargr, maybe - but only as a name. I only have the PDF to hand, and it's the 1990 reprint, and the vargr are not detailed.
Aslan, not mentioned in that edition, and Dark Nebula is 1980.
Adv0 is 1981, mentions both.
Adventure 0 said:
1. The underlying characreristics of Aslan society (pride and loyalty) make behavior much like samurai of the "Age of War"'.
Aslan are presented as playable, noting that quote as the first advice in that adventure.
Adv 2 mentions Aslan and Vargr with name-only references. it's 1980.
Adv 3 has a library data entry, but no stats and a very vague cultural reference. No cultural reference for Vargr, but a lot of mentions including a physical and physical-anthropological note on their not being natural. 1980.
DA 2 name drops Aslan (also 1980).
JTAS Issue 7 has the prior quotes. Samurai Cats has been a trope in the first several presentations. The cat part only in appearance, just like Niven's Kzinti.
Vargr as playables are not in A0, and appear in JTAS 8.
I stand corrected as to origninal presentation of playable aslan - but note that the samurai cat trope was explicitly present there. (Looks like a cat, acts like a samurai.)