It doesn't appear nonprofits are really able to use Venmo ... yet. I found this in the Venmo Help site, so it seems they are planning on expansion to nonprofits:
Our nonprofit account program is currently in private beta, and we are no longer accepting applications from nonprofits to facilitate the collection of donations.
For what it's worth, we use PayPal for one-time and sustaining giving, in addition to the traditional payments.
#FundraisingandDevelopment