Four items in response.
1. Yes, you DO need TWO fan Hubs, and for two reasons. IF you are doing the push / pull arrangement of 6 fans on the rad, that is. First, as I said the RAD FANS MUST be powered and controlled by the CPU_FAN header that uses for guidance the temp sensor inside the CPU chip. The CASE VENT fans all need control from a DIFFERENT header that is guided by a temp sensor on the mobo. Secondly, power limits. The AIO system you plan uses three fans that have a spec of max current consumption of 0.25 A EACH. The limit of power available from any one of your mobo's fan headers is 1.0 A total load, so the first three fans already can use 75% of the limit. Now double that fan count! (You have not told us which fans you would add to the three supplied.) So the RAD FAN system only needs a fan HUB that draws all power directly from the PSU and CAN supply more than a header can.
2. NOTE this. IF you change and go to using ONLY the three fans supplied with that AIO system and do NOT add three more, you will NOT need a Hub for them. Further, that AIO system supplies fans with a proprietary connection system of daisy-chaining all three fans, plus an adapter to connect that to mobo fan and ARGB lighting headers. Sine this means ONE cable for all the fans' motors, you do no need either a Hub or a Splitter for those three fans.
3. You say, "So the radiator fans for the push pull will connect to the CPU_FAN and the AIO pump wire to the pump header while other fans in the case to the CHASIS_FAN header." YES, that is the right way to do this.
4. For the CASE VENT fans (six of them) from ONE CHA_FAN header you WILL need a second fan HUB. You have not specified which fans those will be. But to use SIX from ONE header obviously needs a Splitter or a Hub. To do this job with a SPLITTER that has ALL power drawn from the header, those fans would need to have a max current spec of 0.16A or LESS, and you cannot tell us that will happen. Much safer to go with a HUB that gets fan power from the PSU.
(To be continued - I have a few jobs to take care of.)