Most ClickBank merchants allow DTM PPC.
However, the use of adware and spyware to overwrite cookies is rampant within the ClickBank network, so you're going to get eaten by sharks while you're swimming there.
Further, the landing pages of many (but not all, for sure) typical ClickBank merchants are spammy'ish type pages that G doesn't think are good customer experiences, so be prepared to be hammered by quality scoring algorithms.
In addition, if the merchant does allow DTM PPC, there will likely be many other affiliates bidding within AdWords for the same types of keywords and the same landing pages, so it's unlikely you can get any decent volume working at favorable prices, and therefore favorable levels of return.
I know ClickBank seems like an easy path to newer affiliates, but there's many reasons why it isn't.
Whatever comes your way, good luck with it all!