Do Twi'leks smugglers wear head gear or does the head gear just not show up?
There's a "hide head slot" option that does as the description says.
For example, my scoundrel has some gunslinger goggle armor that she wears, though I usually hide it. Tried disabling that slot for "realism" on Tatooine, since it's so bright and sunny there:
...though I re-enabled it later.