Answer:
There are no privacy issues here; the vendors aren't consumers, nor are they customers. Soliciting the vendors' account information for ACH payments can be more efficient that payment by check, assuming your institution has the appropriate ACH-file-generation features in its accounts payable package. Make sure you have a way to notify the Receivers of the invoices that you are paying with each ACH credit entry you send their way. I also recommend that you generate a pre-note for each vendor before sending any actual dollar entries.