Zigbee supports several different profiles, and they are not all compatible with each other.
In addition, the zigbee standard allows individual manufacturers to add proprietary encoding on top of the standard profiles, which is actually one reason why Zigbee is so popular for security sensors. Many security companies add their own encryption.
SmartThings uses the standard zigbee home automation profile (ZHA 1.2). So devices that use the standard profile can usually be made to work with it. For example, there is one model line from NYCE that will work with SmartThings, and another model line that has proprietary encoding for Control 4 and will not. Both are zigbee, but the profiles are different.
http://nycesensors.com/products/ncz3011c4/
This has nothing to do with SmartThings: it’s up to the manufacturer whether they use a standard profile or not.
If you contact visonic and give them the model number of the sensors, they should be able to tell you whether it is using a proprietary profile or not.