If the code does not require that all CMU cores be filled with grout, then there is not much chance that the builder will do so.  Almost all of the subdivisions that I checked on in Central Florida required the homeowner to use only the builder of record for that subdivision.  What I have found to be true is that the builder will not deviate from the normal way he builds even when I offered to pay for the engineering to use ICF, SIPs, etc.  Some subdivisions will offer a limited line of options and changes to their plans but that does not usually include using a different technology to build the walls or roof.