It's my understanding that hydroforming isn't an indication of quality by any means. It just means the frame is made in sufficient volume to justify the expense of the tooling; in fact it's present on some rather low-end offerings.

Furthermore, from what I understand, it's not likely to be present on top-quality frames, since it precludes fine control of wall thickness, meaning any hydroformed tube is going to have thicker walls than would otherwise be necessary.