You can't get an XBEE to feed PWM into an esc, it simply will not go fast enough. You will have to have a processor that takes a number from the XBEE and converts it into a PWM signal. It will keep on sending that PWM value until the XBEE gives it another value to set the PWM to.
Well it can also be "way too fast" in the sense that it is possible to program the other end XBee to generate PWM signals but the period is typically way too high frequency (microseconds) at least for regular RC servos that typically need appr a 50 Hz cycle or so.
Those excellent tutorials explain that an XBee can be programmed from another XBee to set or return the status of its pins. What you want to have happen can be remote controlled from the other end.
So if there is no additional Arduino board locally, then there is no local autonomous control logic, decisions must be made at the remote end and have take effect by programming IO pins of the opposite end XBee.
In contrast there exist a fun asian module, the RFBee, which makes use of just about the same pinout as XBee, features a simpler radio transceiver, but instead of the extensive "remote control" AT command set of an XBee it allows the user to reflash its internal ATMega168 with user extended versions of its open source firmware, and thus extend the serial functionality with whatever local Arduino IO control operations that can apply to the mapped IO pins. About 30% of flash memory is free for additional code. I figure that particular module could be programmed to generate servo friendly PWM using timer interrupts in addition to functioning as a basic serial radio bee. But again that´s not an XBee, basically only has the same pinout as one.