Hardware Warranty
Does my cracked back cover fall under hardware repairs? Meaning i can use my warranty to get it fixed
Warranty and Apple Care+ are 2 different things.
Apple Care+ offers two incidents of accidental damage every 12 months for a reduced fee that would cover the cracked back.
The regular hardware warranty does not cover accidental damage. You would have to pay the full out of warranty repair / replacement fee in that case.
See here: link->iPhone Repair - Official Apple Support