These ICs are charge controllers, not stand-alone battery chargers. They are intended to be configured and monitored by a host system. The BQ25703A is described as 'multi-chemistry' (including Nicad and NiMH) but the datasheet provides no information on how to use it with anything other than Li-ion. The BQ24780s datasheet does not mention NiMH at all.
To charge a 6 cell MiMH properly the host would have to monitor battery voltage and adjust charge current to match the desired profile (delta-peak, fast charge or trickle charge). The BQ25703A is probably more suited to this, though the BQ24780s might also work if set up for 2 cells (1 Li-ion cell is roughly equivalent to 3 NiMH cells).
Charging a three-cell nickel-based battery pack with a Li-Ion charger
it is possible to charge a 3S NiMH pack safely and to nearly full
capacity with a single- cell Li-Ion charger. The Li-Ion “nickel
charger” can be classified as a hybrid fast/trickle charger, getting
70% of the bulk charge in 5 hours. The charge current tapers toward 0 Amps near
the end of the charge, which reduces the chance of any thermal
issues and possibly provides longer cell life. Most noteworthy is that
the CC-CV method can be used to charge battery packs with either
nickel-based or Li-Ion chemistry with no changes in hardware or