Not necessarily, if you ask my own personal experience. Can be a matter of ergonomic acquaintance!
Without a belt under it, my hakama would just fly away each time my teacher throws me around. The only way to keep my hakama close to me is to tie it's belts around and through my inside belt. Tried all the other ways around and nothing works. Tying the hakama belts alone around my iliac bones creates pain than i cannot withstand.
So it always comes down to very personal somatic and psychic comfort, i reckon.
....This sounds strange and I don't know what health problem causes this. In most koryu and some modern budo like Kendo no one wears a rank belt. If it's a true koryu it does not use the dan system.
For Kendo we just have the dogi and hakama and no pants. It was the same when I trained in Shindo Muso Ryu Jodo.
I never heard of anyone in Aikido who could not keep a hakama on without louping through a rank belt. First time for everything. I assume you have seen a doctor for your painful condition. At least you can do Aikido. I wish you well on that painful condition.