I had managed to run P400 on ESXi 5.1 using hpsa driver, slightly modifying cciss and hpsa drivers and making .vib's from them. The rough translation of my article (original is in Russian) with link to .zip with two .vibs to make your P400 recognize >2Tb on ESXi 5.1 is here:
It will support P400i too, both PCI IDs are remapped. Use at your own risk, no detailed testing was conducted.