You could create a formula that formats the field in one database to match the other, as in the following formula {@SSN}:
replace({database1.SSN},"-","")
Or, if you are using CR 8.0, where the replace function doesn't work consistently, use:
left({database1.ssn},3)+mid({database1.ssn},5,2)+mid({database1.ssn},8,4)
Then you could use one of the databases in the main report and the other in a subreport, and link {database2.SSN} to {@SSN}.
-LB