I've worked with plenty of startups that bring on a top-flight sales person who is referred to as a co-founder, but typically the equity grant is much lower than a typical co-founder (more in the 5% or so range). There are a number of reasons for this, one of which is that the typical first salesperson comes on board after months if not longer of product development work.
That being said, there is a reason that salespeople are traditionally paid on a commission basis. Is there a reason you want to ignore that convention and, instead, detach compensation from being directly tied to each sale? This seems like an odd move, particularly when the prospective co-founder does not see himself as a salesperson.
You can grant equity on a non-time-based vesting schedule (i.e. performance-based vesting based on sales performance), if you are not ready to start paying cash or want to grant equity for some other reason.
But this person is simply untested in this role and you will not know in a couple of months whether he should have a significant equity stake in your company. So, traditional time-based vesting (and particularly with a magnitude of shares like that that would typically go to a co-founder) is a choice you are likely to regret.