Six 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. You plan to use six Lian Li P28 fans on the rad. Their web page does NOT tell us the maximum current each fan can draw. Most fans can draw from 0.10 to 0.25 A per fan max. But the limit of the header is no more than 1.0 A total max current load. With NO spec for these particular fans, it is MUCH safer to use a HUB that draws all power from the PSU directly, and none from the host header. The way those fans are supplied, you connect them together in groups of three with an adapter to plug into a standard fan header. So each group of three can be connected to a single output port of a Hub.
2. NOTE this. IF you change and go to using ONLY three fans on the rad and do NOT add three more, you will NOT need a Hub for them. It is VERY unlikely that each fan would draw more than 0.30 A, so using only THREE on the rad can be handled by the CPU_FAN header. Further, those fans come with a proprietary connection system which can daisy-chain three fans, plus an adapter to connect the group to a standard mobo fan header. Since this means ONE cable for all three fans' motors, you do not need either a Hub or a Splitter for just 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. 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 as noted above we do not know the max current for each fan. Much safer to go with a HUB that gets fan power from the PSU.
5. Your last diagram looks right with one small note. Those six case fans all DO come off one Hub controlled from the CHA_FAN header. It's just to note that ONE of them - the rear one - is mounted as EXHAUST.
6. I note that those fans come with a "controller" that is a little box in a cable with three speeds you can set. Do NOT use that! All it does is reduce the Voltage supplied to the fans so they can NOT reach their max speed. This severely limits cooling ability needed when your system is working hard, and you are doing everything you can to get MAX cooling! The normal automatic fan control system will always reduce the fan speeds when they can for low-workload use, and speed up when needed.
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