Do I need any kind of hazmat certification to carry oil cans in the back of my m984 in Europe?

If the EU has anything to say about very likely. There is also a very stringent vehicle maintenance and modification standard all HAZMAT carrying vehicles have to meet called ADR. If the 984 tows anything Hazmat, then it has to meet that standard too. This is what we’re bringing 4ID units up to standard on in 2016-2017.

The unit should have gotten guidance on this

Yes.

More than likely. A lot of it will depend on country laws. You'll need to check with your Motor Sergeant and your Command.