My son napped in his seat/bouncer. It was unavoidable and yes there were times when I just lay down next to his seat and rested instead of trying to move him into his cot/basket. I can remember carrying him in his seat to beside my bed and dozing with my face hanging over the mattress to check on him every couple minutes.
I think if you are near your little one, if it's for a nap (say up to an hour) then that should be fine but never for night time or longer sleeps. I never put him in his seat with the intention that he fall asleep but sometimes if he dozed off I dared not wake him. He was never left alone.
I remember thinking at the time about car seats, they sleep in them so it's not hugely different to a swing/bouncer.