I can only give my experience and this is a very old debate. The only account i have ever had banned (i was fortunate to miss the recent suspension wave that hit in May as i was overseas for a month prior and a couple of weeks following the May event) was on a computer i only use a VPN on.
Why did i use a VPN at all? ISPs where i live have started forwarding cease and desist letters to customers from Warner Bros, etc. regarding torrenting movies. I got one. So i now only torrent through a VPN on a small spare laptop i have (it runs 24/7). I also had WoW on this computer so i would utilize it to bot with 1 account. My plan was to never disconnect the VPN (as i said it torrents 24/7). Woke up one day and the VPN wasn't connected (must have disconnected overnight) but my toon was still leveling up (my bad for having HBRelog on there). Re-connected the VPN and a few minutes later i was notified of account closure.
It was a fresh account, only had 1 toon on there at ~level 80 (hadn't even purchased WoD and got MoP for $13.50 with their 50% off offer) so no big deal. Could be a huge coincidence, who knows, but i will always steer clear from botting on VPNs now.