Well, it's a dump of 1/4 of the data, so maybe 1 out of 4 chips, you don't get 3 meg rom chips.

All I can tell you is the banking hardware maps to
0xA13000 - 0xA1303f in the 68k map.  If you write data to those addresses the offset is used to calculate the bank (the data written doesn't seem to matter, just the offset)

writing to a13000 sets the bank to 0, writing to higher addresses increases the bank / base (which part of the cart appears at 0 in the Genesis memory map) in 128kb steps.  eg. writing to a13002 sets the base to 128kb, writing to a13004 sets it to 256kb.  This allows them to bank any game rom at address 0 before jumping to it.

The best way by far to dump it would be to open it up, stick the chips in an eprom programmer and read them that way, although if they're custom packages inside the cart that may prove to be tricky.  Beyond that you're going to have to find some way to fool the dumping sofware you have into changing the banks.

It can't really be considered a good dump at the moment because it's incomplete.  If you do decide to open up the cart and dump it that way then i'd be more interested in a dump of each individual chip in the native format that the eeprom programmer gives (not pre-byteswapped for emulators).