Is there any way to reduce the large fat pooch (at the pelvic area) that is left after a hysterectomy?

The fatty pooch that you refer to is normally a hysterectomy scar that tightly bound down to deeper tissue with fat and skin piling up above the scar tissue, leading to an overhang.  Obviously, a tummy tuck would remove this and other skin and soft tissue above it.  However, if this is the only problem, then this bit of skin and soft tissue can be surgically excised, but this will lead to a longer scar.  A very quick and efficient way of dealing with this type of anchored scar tissue is to liposuction the area above the scar, and then use a "pickle fork".  This is a surgical instrument which looks like something you would pick up a pickle with at a fancy party.  The pickle fork is used to release the scar tissue binding the skin down to the deeper tissue.  This plus liposuction can usually remove not only the overhang, but also the depressed scar with minimal incisions and quick recovery. 

Often after a C-section, the scar and skin below tightly adhere to the abdominal wall, while the looser skin above can have fullness and prominence. In some cases, this is an ideal indication for a mini-tummy tuck. If the fullness is below the scar, liposuction may be the best treatment. 

Is possible to correct abnormalities of your Mas pubis. It really depends on what it's also going on at your C-section scar and with your abdominal wall. I recommend several board-certified plastic surgeons.