haha, my hospital didn't even check to see if our seat had expired or if we had her in it right, or do an oxygen test or anything. we strapped her in, they took a quick look and let us go. and, for the record, it WAS an expired seat, AND she was a preemie, so i'm doubly surprised in retrospect.
(in our defence, she was 5 weeks early, we didn't own a car and had been planning a homebirth, so carseats were not even on my radar. my MIL gave us the seat for an emergency, but since i didn't know anything about seats, i didn't even realize seats could expire. i knew it was old, based on what i saw other people using, but when i nervously asked the nurse about it when we were getting ready to leave, she didn't even blink... the darn thing was so old it didn't even have a 5 point harness! i'm mortified that i ever put her in that thing now... thank god for MDC!)
sooo, anyway, i think it varies incredibly from hospital to hospital. you could end up with a real PITA nurse who doesn't realize convertibles are safe for infants, or you could end up with someone a bit more "relaxed."