Dishman -
Welcome to FOG. The Domino is a great machine if you want to do a lot of mortise and tenon type joinery. Great for cabinets, desks, tables, chairs, chests, etc. It's one of the best tools I have after the basic power tools if I don't want to do traditional mortise and tenon joinery with hand cut tenons on a bandsaw and mortises with a drill and set of chisels. It will definitely make you more productive and likely more confident in your work across many projects.
You may know that have some guidelines on spacing that I'd be mindful of that for child safety. See
http://kidshealth.org/en/parents/products-cribs.html
I'd also consider the look you are thinking about for the crib. While you could make the the entire crib with slats top to bottom rounded over to the size of a domino, I think a more classic look would require a larger rectangular slat with a smaller domino in the end and then going into the rails top and bottom. So I'd probably start with a design you like and then investigate if the domino would be the right tool.
With slats likely to be 24" plus in length, a routed slat that would fit in a 10mm domino mortise would be about the smallest I'd go with a top-to-bottom oval slat for strength. I generally like a tenon with a shoulder which is why I was thinking the rectangular slat might be a better choice. Birdhunter's crib looks to have substantial slats and would give strength and space for a domino in each end. If you want a crib with less robust slats, the Domino might not be the best choice. The minimum domino size is So I'd think about those considerations and start with a design to determine if the Domino is the right choice for your crib.
Here's the sizes of Dominos, so take that into consideration as you are working through the design -
http://www.highlandwoodworking.com/festool-domino-joiner-model-comparison.aspx
The Domino is one of Festool's most 'breakthrough tools' and certainly has great utility for lots of other things, but if a crib is the first, think through your design and if the Domino can help you execute that design.
Look forward to seeing your progress -