DS2715 NI-MH Charge Controller Help
Based on the table "RECOMMENDED DC OPERATING CONDITIONS" on page 2 of the datasheet you provided, there should not be any problem with connecting 12 V to the IC, as the maximum recommended voltage for Vdd is 16.5 V.
The IRF has a blocking voltage of -60 V (see 1), so it could handle the 12 V as you already mentioned.

The DS2715 has a presence detection that is based on the voltage on the Vbatt pin. On page 6 of the datasheet under section "PRESENCE" you can find one of the conditions needed for the detection of a connected battery pack is Vbatt > Vopen. Vopen is fixed to about 1.65 V (page 3). Without a connected battery pack the voltage Vbatt should be higher than this threshold to avoid a false detection.
In your case the voltage divider was designed for a 6-cell battery pack, where i assume that the voltage on Vbatt is 1/6 of the supple voltage (6 V), therefore the voltage is lower than Vopen.
If you apply 12 V to the circuit, the voltage Vbatt will increase to 2 V (> Vopen) and the IC should not detect a connected battery pack.