The 10" would need to have the optional output board to provide VGA out. They didn't originally come with that option.
The 7" radars are linear processed and cannot be directly connected to a 10" (logarithmic processed) but like others have already said you can have the radar go to the 7" and then network in 10" units into the system. If someone changes the cable on a 7" radar and attempts to use it directly to a 10" will find problems when they actually use it.