They are sort of the same.
You are correct in the manufacturer part. IMR used to be Dupont, and H is Hodgdon.
They are not the same. Hodgdon is slower to some degree.
My best load for Garand (.308 Winchester) is 168 grain HPBT and IMR 4895, about a "middle" load.
For .30-06, the charge will be a little greater. Check your loading manual.