This seems to be an allusion to Ovid's Amores 3.7, in which Ovid reproaches himself for not being able to sexually please his mistress, stating that it was "as if his members had been rubbed with a chilling hemlock and knew no more the way to do their duty."

I am not familiar with Elizabethan poetry, but a quick Google tells me that male sexual ineptitude is a central theme of this particular poem by Nashe. Because the themes of the two poems are so similar, I'm going to posit that this is not indicative of a societal level association of Ovid with hemlock, but merely a clever allusion on the part of Nashe.

Here's a link to the Ovid poem in both Latin and English, hope I helped.