It's definately possible with FMP 10. You can probably do it with FMP 6, but you'll have to research the documentation on how to use FMP 6 to send email. It has the capability, since I can find it in FMP 5.5 (I don't have FMP 6).
Here's a basic outline that'd work in FMP 5.5 and FMP 10 (Thus, presumably it'll work in FMP 6)
Define a calculation field cDate6Mos as
Date ( Month(yourdatefield) + 6 , Day (yourdatefield), Year (yourdatefield) )
Define a date field ReminderEmailed
#Exact script steps will vary depending on whether you use FMP 6 or 10:
Set the following script to run each time the file is opened:
Find all records where cDate6mos is < the current date and ReminderEmailed is blank
If any records are found, loop through them sending the email and using Set Field to log the current date in ReminderEmailed.