Yes, there is a way. There's a bunch of ways. xP It just depends on which you want to use.
The EASIEST way would be to create a plugin that will fetch user info for each thread displayed by the forum. BE ADVISED, though, that this will create an additional query for each thread loaded with the forum display. XD Not somethin' you want, probably.
Next easiest would be to execute a custom query with a JOIN, something like
SELECT thread.postuserid, userfield.field17 AS maritalstatus FROM thread, userfield WHERE thread.threadid IN (0,$ids) AND thread.postuserid=userfield.userid in the 'forumdisplay_query' hook. With the results assigned to an array $marital_status_array (as userid => maritalstatus), you could put <if condition="array_key_exists($thread[postuserid], $marital_status_array)">blahblahblah</if> in the
threadbit template.
If you're willing to go through that kind of work, tell me, and I'll post some step-by-step instructions.