As in, were they fast enough to be used with other layouts? Yeah, but this was back when letters were dictated- secretaries didn't go switching to dvorak. Any typewriter could technically use any layout, since you'd just have to swap out the characters.

The biggest advantage of the selectric was that you could swap out the ball to get different characters or fonts. The ability to get italics was a pretty big deal.

Here's Bill Hammond talking about them: https://www.youtube.com/watch?v=bRCNenhcvpw