I contacted Tim with our Training and Education team. There are no Ariba certifications yet, but we are planning to offer certifications in the future.
Ariba training is available through training.sap.com (where you will find the rest of SAP training options). Ariba training includes live virtual sessions as well as self-serve content on the SAP Learning Hub. In the next few weeks, Ariba will start its first Learning Room as well.
I hope you find this helpful.
Ariba Exchange Community Manager