Check with a real estate lawyer. I'm not a lawyer, so this isn't legal advice.
If you're not on the mortgage, I'm not sure you'd be notified. However, there probably are instances--state by state--in which partners or husband and wife both might be required to be notified, even if both aren't on the deed. Again, I'm not sure; you have to check.
As for a co-signer being added to the deed--again, I'm not a lawyer--but the deed and the mortgage are two different items. However, it depends on how the property is held--tenants in common versus tenants in the entirety, for instance. With tenants in common, the other person could sell or assign his interest in the property to someone else. So, and I'm just guessing here, if your ex-hubby is interested in refinancing the property and pulling some money out and his current wife/partner is going to be co-signing, it could get very complicated. So...as already said...check with a good real estate lawyer.