Expanding on Alex M's reply, in manual flash mode accessed through the custom menu, you can dial down power to 1/128 and pre-flashes are not emitted. In this manual flash mode, it doesn't seem possible to put the camera into continuous drive mode (requires a separate button press for each exposure whatever drive mode is set on the dial). However the recharge time is all but instantaneous and is likely to be well under most strobe recharge times. I managed to get between 2 and 3 exposures per second but that is a reflection of how fast I can press the button rather than recharge time and might be a bit slower in a housing. I assume that in this mode external strobes trigger but output has to be adjusted manually.
There is also a commander flash mode which is intended for controlling external strobes and it is this mode which I would assume might be best for use in a housing with external strobes? In commander mode, the internal flash has to be raised, but can be set to TTL, manual (down to 1/128 power), or to fire pre-flashes only and then nothing itself for the actual shot although remote slaves do fire. The same limitation on drive mode appears to apply for commander flash mode as for manual flash mode. I am not at the moment clear how the wireless control of external strobes in this mode works and so whether optical triggering and TTL control will work for third party underwater strobes. Others may be able to enlighten me while I try to find the answer elsewhere.
However the bottom line in relation to Alex's original question is that it is certainly possible to dial down flash power on the D7000 to produce negligible recharge times.
Of course all this is a bit theoretical as I don't (yet!) have a housing Alex.
Not sure if I missed this in the review but I've been asked by a few people, can you manually dial down the camera's flash on the D7000 and, if so, at minimum, how fast is the recharge time?