I have all my nails grown out, and I strum both with my index, and my thumb at different times, if I want a slower clear single strum it sounds better if I use my thumb, I strum quicker with my index, but sometimes I use my index and my thumb at the same time while I'm strumming, I use my middle finger for chunking, but sometimes I also use it for upstroke strums. I'm also getting pretty decent at what I think aldrine and them called a triplet strum, where you use index and thumb for an up, up, down combo strum. The nails give me options as well, so i can choose single chords or single strums in fact to accentuate with the attack from the nail.
I've used this line before, and I think it should be my own special phrase now, "Never limit yourself" try using thumb if you never do, use index if you never do, it's just another thing to add to your uke arsenal for use when YOU so choose. I'm always trying to gather as many techniques as I can, because I think it will make me a more balanced player.