The iRule Editor checks the product features from the System.SystemInfo.get_product_information() method to determine whether GTM Rules are supported. It looks for the feature "GTM Rules".
I just ran the method off of my v10.1 RTM box and the following GTM features were returned from the SystemInfo.get_product_information() method.
GTM Failover To One Data Center
GTM Monitors
GTM Rules
Can you make an iControl call to determine the product features returned on your system? The SystemInfo perl sample in the SDK works nicely and you can run it from your BIG-IP CLI. Let me know if you need a copy and I'll post it.
-Joe