Yes, they were in the "Black Codex", a small pamphlet in the 2nd Ed. box set.
I think they maybe had datacards for the Bikes too?
Pretty sure, yeah.
Their best coverage was actually in the Epic Space Marine 2nd ed Warlords box, which also contained the 6mm Ork rules (because Orks and Squats were both lead by Warlords, of course). There was more fluff about the Squats, their Hearth Worlds, and their culture than any other GW product I know of, and Epic gave them a slew of unique vehicles ranging from gyrocopter gunships to a variety of lumbering super-heavy vehicles that could give a Warlord titan a hard time to the Overlord airship, an armored zeppelin-style gun platform repurposed from craft built to "mine" the atmosphere of gas giants.
Good times. Played pretty well on the tabletop, too. Sadly there wasn't much new stuff that was suitable for 40K gaming, so Epic failed to save them from their current near-oblivion in the setting. I think they've currently got what, two figs in the Necromunda Forge World range? A sad turn of events.