You just said it yourself: half
droid. He wasn't a droid, he was a cyborg.
Nicho was no different (physiologically), from Darth Vader.
Y'see, Nicho would've been born human. (He was
human, right?) The cybernetic components would've been added to him, but his organic structure would've remained, and with it his Force talents.
The impossibility with CotJ isn't Nicho, it's Callista.
As long as Nicho retained organic components, he'd have been Force-sensitive, but when Callista was inside the Eye of Palpatine
, her organic body would've been completely gone. According to the midichlorian theory as widely accepted, that'd be impossible (no body -> no midis -> no Force).
That bit of EU just adds more strength to the "midis as symptom" argument.