What an excellent question Diego! Congrats!
Yes, things get very interesting with multiple default gateways in OSPF! Yes - if the two different default routes have the same cost - they might get load balanced, but things can get weird fast!
For example, what if one of the default gateways is in a different area! Now you will not see load balancing by default because OSPF prefers intra-area routes over inter-area routes!
Yet another consideration here is the external metric type set in OSPF. Remember, you have two types. - a type where the cost through the local area is ignored, and a type where the cost is incremented as the route travels in the area.
OSPF is fun!