identify if Filevault is enabled on remote Mac
Can you run a command line tool, such as fdesetup?

$ sudo fdesetup status
FileVault is On.


fdesetup also accepts the verb isactive, which returns 0 if FileVault is enabled (checking a return value is arguably more reliable than reading the text):

$ sudo fdesetup isactive
$ echo $?
0


fdesetup does require root access, which might be a problem.

You could also run diskutil cs list and check for the encryption status. The exact wording you're looking for is a bit complicated because of all the different possible combinations, this script might be a good start.