The only reason I could think of for hybrid is low end toque to get the beast off from a dead stop faster.
I drove a Porsche like this and it damn near killed me being unprepared for the initial acceleration.
No clue if that would be a benefit in a tank.
I actually do agree. If a MILITARY-RELATED case can be made showing that a Hybrid has more advantages than disadvantages (which are many, starting with complexity), in a combat scenario, then it would make sense to go that direction. For starters, a tank able to operate on batteries would have a far lower heat signature than a tank with an active engine, something we in the battlefield worry quite a bit about, these days.