The PPSA emphasises the priority of security interests, regardless of whether the secured party holds title to collateral.
Upon the receivership or controllership of a grantor, if a security interest (first security interest) has priority to (for example) a lease or conditional sale by retention of title (because the lease or retention of title sale is unperfected, or is perfected second and lacks PMSI super priority), the receiver or controller can sell the leased or retention of title collateral over which the first security interest has priority. It does not matter that the grantor under the first security interest does not own title to the collateral.
The PPSA clearly overrides the nemo dat principle to this extent, to facilitate its treatment of various transactions, including title-based transactions such as leases, as security interests. See Chapter 24 (Enforcement of PPSA security interests) for discussion. Indeed, there appear to be forceful arguments that the PPSA does even more damage to the nemo dat principle, by permitting (if the arguments are correct) grantors with mere "possessory" interests such as lessees under PPS Leases, buyers under conditional sales that are security interests or consignees under commercial consignments, to sell collateral and extinguish the interest of the lessor, seller or consignor. See the discussion in Chapter 21 (The Extinguishment Rules).