Dear Min,
It basically depends on whether you want your product to be ZigBee compliant (with the ZigBee Logo) or not. If you do not want your product to be ZigBee Compliant, you do not need any license or certification to sell it, but you cannot put the ZigBee logo on it.
Moreover, the BeeStack solutions have been tested to interoperate with other vendor’s ZigBee devices, so if you base your solution in any of our projects, it is likely to be interoperable too. However, it will depend in the other devices’ settings such as security and profile used.
Regards,
AngelC