To some extent, cardio machines are like other fitness tools such as weights, KBs, etc. A lot of what matters most is really in how you use them. If you step on and do a long slow slog for 45 minutes or if you always employ the same one in the same way--not so great. For interval type stuff, as parts of WOD-type circuits, for variety, and suchlike, I don't see why you couldn't make decent use of them. I usually don't use em, except C2 rower, (I'm usually at a CF gym that doesn't even have them), but I was in a conventional gym last week with some other CF-minded folks and did a pretty good workout that, in one of its segments, incorporated one of those stepmill machines (with the revolving staircase) maxed out at level 20 (huff, puff). IIRC, we did something like five 1-min. rounds of stairs, squats, situps. Several "regular" gym patrons wondered what in the world we were training for. I gave a different answer each time. Fun. Fitness. Life. I think they got the gist of it, though, from our intensity and the looks on our faces.
Anyhow, the point was that you can probably integrate a lot of these types of machines into your WOs; it's just about how you do it.