It depends.
If you're just creating hardcover volumes for your own library, you're good to go across the board.
If you're looking at creating volumes to sell, that gets trickier. The material is all in public domain, but you would want to make sure the scanners (and editors, if somebody else edited the scans) are good with it. Anything I scanned, for instance, go for it... I do not believe my scanning or editing is transformative to the work, so it's still PD. But some scanners may feel differently, and in any case it would be just basic courtesy to check with them and credit them.
Please note that this applies ONLY to the scans of the original material. If you were looking at commercially printing some of the collections of specific strips that have been compiled, the stories are fair game within the limitations listed above. But the editorial material is not; you couldn't reprint the introductions or redesigned covers or whatever else was added without the permission of the people who created it, it's all far too new to have fallen into the public domain. I'm not sure if anybody has actually formally set up some sort of Creative Commons license for their material like that, one the ones I've done with Yoc we would be very unhappy if somebody tried to sell the material.
It's also worth noting that some of the material we have here is public domain but the characters are still under trademark; if you were to put out a collection of, say, Blue Beetle, Captain Marvel Jr., or Plastic Man stories you would have to be very careful in how you did that... just look at all the limitations on stuff derived from Steamboat Willie that's turning up this year. I would strongly recommend not even considering something like that unless you talk with a good lawyer first.
