To answer we need to know the exact mobo you have. AND the exact FANS you want to connect. The single mobo ARGB header will have a limit on how many amps current it can supply to the total connected lighting load. Fortunately the Deepcastle website for the 3-fan 360 mm rad version of that AIO system gives clear info on its components: the LIGHTS in the PUMP consume at max 2.25W, and the THREE rad fans' lights consume up to 7.2 W. Since these are 5 VDC lights, those translate into 0.45 A and 1.42 A, total about 1.9A. (IF you have the 240 rad with TWO fans, that is reduced to 1.4 A total.) So we need the LIGHTS power requirements from all your other ARGB fans, which we can hope to find from their web page, and the capability of the mobo header. Then we can tell you whether all of that power can come from one header. That's where the limit is - the simple logic of whether the splitter and fans can be used this way is YES, that is not a limit.
Just in anticipation, IF it turns out the electrical load is too high, there exist powered ARGB Hubs you can get that can link loads of lights to the same control signals, but get the required high power directly from the PSU.