How is the engineered attached to the slab?

Not sure at this point. But, lets assume worst case that it is glued down.

Either way in a pantry as long as heights are OK.

Most factory cabinets are minimal height & built to fit on top of flooring (retrofit)

Most custom cabinetry is built taller to be installed before flooring.

Permanantly fastened flooring, like glued down engineered goes under cabinets. Temporary floors, like floating engineered, goes after cabinets. But the cabinets have to be set at the finished floor height with shims.

I would just install the pantry cabinets on top of the engineered flooring.