I saw Mudvayne bassist Ryan Martinie did it, and it sound super cool(it is abit watery). I am in a band, and our song got slap and pop, but at the same time we got fast riff for picks in one song i won't have time to get a pick when the riff change, so i use the nails instead and i can go as fast as the pick with it plus I like the sound lol.

I wonder though, whether this kind of playing is ok or not

It's ok if it's ok with you

yea, it is ok with me, i can keep constant rhythm with it while playing fast.

I wonder whether anyone else did it btw?

If it's okay?

We're not easily offended. :P If it gives you the sound you like, then it's worth the use. Just make sure you don't rip off your nails. I tend to strum my acoustic bass with my finger nail first when I use chords.

As long as you make a crazy face when you do it, it should be fine.

I actually hold the first digit of my index finger like a pick and strum with it and that does a good job. I keep the nail of that finger longer than the rest, but only slightly.