As a practical matter, I think you'd be pretty unlikely to blow one of the fuses under most circumstances. It's rare that the starting battery would be completely doornail dead, and the current that flows is determined by the charge acceptance rate of the battery at whatever voltage ends up there...which will be lower than the resting voltage of the house battery, both due to voltage drop in the wiring between the two and due to the voltage of the house battery drooping under load.
In the more typical case where the chassis battery has some charge but not enough to turn the engine over, it's still going to provide a reasonable amount of current to the starter when both are combined.
