Just for the record, I've done it and it works.

The N900 runs warmer: normally it's 33 C when idle, but with host mode it's at 38 C. This goes up to 43-44 C while it's being used intensively.

One thing still doesn't compute, though: if the N900 can provide at most 200mA, and the hub takes one unit of 100mA for itself, there is only 100mA left for the devices. A USBEthernet adapter uses >100mA, so how is it possible that it works? Note the hub is passive, i.e. this is before connecting the external +5V. The only possible explanation is that the hub does not reserve 100mA for itself. My understanding of "non-compliant" was that it gives as much power to the peripheral as needed; I guess mine is "doubly non-compliant" in that it doesn't reserve 100mA for itself.