Yeah ive done it with a 1.2mx60cm veg tent inside a 2mx2m flower tent , you will need to build light traps on your intakes of veg tent if passive so it doesn't light up the flower area in dark period.
Not ideal but I never had issues with it. I would avoid it if possible but you gota work with what space you got.
A light proof fabric throw over wouldn't hurt either, depends on the tent but a lot of them leak a bit around the stitching.