From a (superficial) reading on the civil registro website, the civil union offers many of the legal benefits of marriage without as much paperwork
However, I didn't see anything stating how earnings would be treated during the time of the partnership.
If you're married here, what you both enter into the marriage with remains yours. But what is earned during the marriage is a 50/50 split. I don't know how it's handled in a civil union.
You may want to go there and ask - I've actually found them to be pretty helpful there