Do I still need to learn about Zigbee if I am using RapidConnect?
It certainly can't hurt! RapidConnect firmware and tools provide a level of abstraction to shield you from the "nitty gritty" and let your developers focus on your products' features and unique value. But your Sales and Support teams will likely still need to answer questions from your customers and help with troubleshooting in the field. You can decide for yourself how much knowledge your require to develop and sell your product, and we can recommend resources that may help after discussing your product and business needs.
As a start, you can review our Zigbee 101 and Guide to Zigbee 3.0
If you intend to write code on a Host MCU to implement the RapidConnect Serial Protocol, it will likely be very helpful for your development team to at least review the Zigbee specifications here.