Is the sheath of MC considered an EGC for bonding?
Normal MC, nope. There are special types that are okay, M-Cap and such, not everyday stuff though.
250.118(10)
Type MC cable that provides an effective ground-fault
current path in accordance with one or more of the
following:
a. It contains an insulated or uninsulated equipment
grounding conductor in compliance with 250.118(1)
b. The combined metallic sheath and uninsulated
equipment grounding/bonding conductor of interlocked
metal tape?type MC cable that is listed and
identified as an equipment grounding conductor
c. The metallic sheath or the combined metallic
sheath and equipment grounding conductors of the
smooth or corrugated tube-type MC cable that is
listed and identified as an equipment grounding
conductor