There’s two issues with this.
A) the current schema (https://iot.mozilla.org/schemas/) doesn’t have Keypad thing type. This would requires changes to the schema and the gateway.
B) once a thing type of keypad was created, then the zigbee adapter must be modified to classify keypad zigbee devices as keypad things.
You should raise an issue on the Github gateway project and request a keypad thing type.