Yes, the Mini-Module just says they are servants of "some dark lord of the lower planes" which suggests Evil but they could also be NE or LE.
It's ages ago, but I vaguely recall Casimir made them CE demons in his first draft and we just stuck with it.
All of the new monsters in The Halls of Tizun Thane with stated alignments are Chaotic (Nandie CN, Nandie-Bear CE, Gu'en-Deeko CN) and the humans too (Tizun's guards-turned-bandits are CN apart from one, Ulgon, who is CE; his brother Diker Thane is CN and his half-brother Sega is CE).
The Green Goblin, Shadow Dancers and a few other NPCs don't have alignments stated.
It would seem weird for Shadowdancers to be Lawful Evil surrounded by all those Chaotic characters. The adventure is basically an oldschool "Nest of Chaos" the PCs' party stumble upon.
That said, I could see the Shadowdancers being generic fiends being generic fiends without the (demon) subtype and maybe "any evil alignment" or "neutral evil" instead of CE, but I'm fine with them as they are.
Heh. Great minds and all that.
I also checked on the alignments of Tizun Thane (TT) creatures to see whether that could lead to some clue as to the shadow dancers' (and Tizun Thane's) alignment, most notably on Diker's (DT), Sega's (ST), and Thraaak's. Didn't get me anywhere and flaming nuisance that gu'en-deekos don't get the alignments of the brains they eat.
I pondered giving TT an alignment different from DT and ST because "plotting to overthrow" could suggest such, but that left LE or NE so that was no good. I wonder whether Mr Fiore had an alignment for TT and SDs in his original concept, although that may well have been "Chaotic" because of OD&D notions.
When I (very recently) found out about Howard's
The Mirrors of Tuzun Thune (
here and
here) things started to look up (because Cthulhu) but that, too, didn't really get me anywhere, because "alien evil" sort of made me think of Moorcock ("chaotic") instead of D&D.
In the end, I decided to go for (uniquely) "ALIGNMENT: Evil (See below)" and then added a note along the lines of "alignment may depend on that of the dark lord SDs serve" and hinted at "evil, alien dimensions", which, admittedly isn't ideal for many reasons. A bit like your suggestion of "any evil".
Anyway.
CE and "demonic" does seem to suit the SDs better than LE and "diabolic" because murder and blood and, dare I say it, Vance's demodands.
Now that we're talking shadow dancers: I noticed you made them immune to "spells", which I also did.
However, on reviewing my conversion after reading much of his thread, I noticed that the original (WD18) actually says this:
From White Dwarf 18 (GW, 1980) (p. 18)
Note the exact wording where their immunity is concerned - and the emphasis on "attacks"!
Could this be read as that shadow dancers are immune to magical
attacks as opposed to
spells, meaning that
Magic Missile,
Fireball, and the bite of
Mordenkainen's Faithful Hound wouldn't affect them but that, say,
Reverse Gravity or
Repulsion (Stone Shape, even?) would?
Many, many, many cans of worms?