ZIGGS IS NOT AN ADC, NO MATTER WHAT ROLE HE"S PLAYED IN
Period.
He's this mystical thing called an APC, they build AP and Carry, instead of building AD and carrying.
He's also not a marksman, as that is what I think you actually meant to put there.
As far as bot-lane diversity, other 'interesting' picks bot-lane include:
Kennen (He can be an ADC or an APC).
Zed (Yes, I've seriously seen high ELO players pull this in S4).
Yasuo (Also S4).
Ahri (S5, in place of an ADC, not as a support).
Bard (Shortly after people discovered he can be played as an AD bruiser).
Malzahar (AD build in S4).
Nidalee (Odd niche pick, and no she technically isn't an ADC).
Twisted Fate (Absolutely not an ADC, although an AD build does sometimes work).
Azir (S4, still saw this off and on until the dash got nerfed).
Yes, Kennen is the only one who's been see in pro play, but pro play is not 100% of high ELO play.