Yes, it is an issue. The impedance of the three PU's should be similar for consistent volume across all three PU's . At least within 25% or so. Any differences after that can essentially be balanced out by height adjustments.

There is the phasing issue, where the SC is opposite phase to the HB's. That caught me when I first wired it up. Also if you are splitting the HB's you will need to be aware of the magnet polarities if combining one coil from the HB with the SC so as to continue a virtual HB operation in positions 2 and 4.

On mine the IBZ DiMarzios clock in at above 8k. Not gunna find a SC with that impedance... so I just have to adjust PU heights and put up with the volume difference.... Then again having a low output option into a OD amp does offer more tonal ranges.