The first half of your statment regarding the LE is absolutly correct (for LE boards version 3 and up).
If you are planning to mount the LE-RX inside of the SSR4-DMX and plug it in place of the RS485 chip, chaining to downstream SSR4-DMX will not work. If you use an "external" receiver and have the output from that receiver go into a SSR4-DMX, then yes, you can chain to another SSR4-DMX.
Larry