Aluminum Cooper Corrosion

Do a Google search for "copper-aluminum joints". There are 19,500 posts offering information about these connections.

Most likely your barrels will suffer, with disturbing consequences of the beer, wine, or spirits within. Oh, sorry, perhaps you meant "copper", rather than "cooper". Nasty bimetallic corrosion - one of those electro/galvanic types of thingies. This is also bad for beer.

Internally with oil not a problem, externally you have the possibility of corrosion dependent on ambient conditions.

What happen..corrosion is some of the more impredictable thing that you may deal with...If you have a joint between two metallic components you are bound to encounter corrosion-related problems. Although details will be dependent on the details of your oil and hydraulic part of your pump dispenser. If I were you, I would try to avoid a direct metal-metal contact, perhaps including an appropriate nonmetallic plastic in-between the metals.

The aluminium will dissolve if such a system is presented with an electrolyte. Oil isn't one of these; it is non-conducting. There is a risk, though it is probably small in this particular case.

Galvanically-isolating pipe fittings are available.

If the oil can be kept free of water and is not ionized(check this out with the supplier of the oil to determine this), then corrosion inside the piping system due to galvanic action should not occur. It should be possible to estimate the concentration of water in the oil below which the oil is "inert". As far as galvanic corrosion occurring on the exterior surfaces of the piping system, isolate the Al from the Cu by using a non-metallic separator of some kind between the two metals.