Just like if an eVar was defined twice in an image request, it's going to only take one of the values. I don't know which one it takes, but it probably shouldn't matter since your data quality will be pretty tainted either way.
I would advise concatenating the same eVars into the same value with a delimiter, so you can classify those values later on. You can also consider using a List Var, which can accept multiple values. However, they cannot be in two separate variable definitions in the same image request.
Either way, you're going to want to concatenate them before they're send to Adobe data collection servers.