Ungrounded outlets are not a problem per se if they were installed according to code when built. However using three prong outlets on an ungrounded circuit without gfci protection is an issue.
You have two code compliant options in this situation 1. install the correct two prong outlets your system was designed for or 2. add gfci protection and label the outlets as such.
Surge protection is primarily designed to protect from utility issues that originate outside the home and will do nothing to alleviate this issue.
If you do in fact have the grounded outlets installed ( you most likely do) by advising anyone to install a surge protector you are admitting in writhing that you have a defective electrical system.
If you have a correctly installed electrical system you are advising your customer of a defect that does not exist. I don't think it is a good idea to promote the idea that your property is somehow substandard or improperly maintained if this is the case.
In short determine if you have a compliant system. If you do you have no further obligation to disclose a defect that does not exist.