If you want to use the built-in Canon RT radio system, then you need a unit that speaks the Canon RT radio protocol.
The only gear, aside from Canon's ST-E3-RT and 600EX-RT that does so, are new units from Yongnuo. They've built their own clones of the 600EX-RT and ST-E3-RT, and both are compatible with Canon's gear, but have slightly different features set.
In addition, Yongnuo has also released the YNE3-RX receiver that can be used with the Canon 580EXII, 430EXII, 320EX, and 270EXII, as well as Yongnuo's own YN-568EX/II, YN-565C/II, YN-467CII, and YN-465C (and, one assumes, any eTTL-compatible flash that can be controlled from the camera's menu). These YNE3-RX receivers can handle the ID codes and groups, and provide eTTL, HSS, and 2nd curtain sync, as well as remote power control with Gr mode for these flashes. Early reports also say that the YNE3-RX supports Supersync (aka tail sync, HyperSync), like the YN-622 triggers.
Be aware that there have been some teething issues with all these new RT units. This is somewhat typical of Yongnuo--they tend to make early adopters into inadvertent beta testers. Early copies of the YN-600EX-RT and YN-E3-RT seem to have battery drain issues.
If you are new to Yongnuo gear, do some research, and learn about how to read manufacture date codes, and who the reputable retailers are with good return policies. I'd say keep an eye out on the Flash Havoc blog, and the POTN messageboard's thread on the YNE3-RX.
Shanny is working on an RT-compatible flash as well, but hasn't yet released it. Their YN-E3-RT clone is out.