Can I use olive oil instead of vegetable oil for this cake?

I think it would be delicious with olive oil.

I think olive oil would work fine. I personally enjoy the flavor of EVOO even with chocolate. I have even used it in brownie mix and cake mix, and they have turned out delicous!

Yes, however olive oil will impart more flavor than a neutral corn or canola oil. I would recommend a "lite" olive oil if you have it. Flavor aside, the olive oil will act as the necessary fat to make this cake work.