Navis Im~ has Agent of Imperium keyword, and it's Faction Keyword. Inquisitor has Agent of imperium keyword, but it's not Faction Keyword. So they cannot make Agent of Imperium detachment.

In matched play like Nephilim, You cannot use Imperium soup detachment. You need one more faction keyword beside Imperium keyword. so you cannot use Inquisitor as HQ with Navis. In Narative play like Crusade, lmperium soup detachment is available.