Nearly all brands of diapers these days have those crystals. To the best of my knowledge they're inert and pass right through (eewwww). They're used in gardening a lot also to keep water in the soil (one tablespoon of them absorbs about 2+ cups of water, if given enough time). If you're super concerned about the crystals, probably the only real option would be cloth diapers (3up + the plastic shorts over). I have to admit, I researched the crystals about 8 years ago, and have no recollection as to what I found...meaning it didn't set of any alarms bells but I have no memory of the results either.
We found that Huggies Overnights worked the best for us. (Diaper Service was too expensive for us at the time and I was NOT boiling diapers on my stove. We had a tiny apartment, and the smell!!)
However, our son had a very large bladder, so right before I went to bed I would always change him into a new one regardless. It DID do wonders for his sleep...he can briefly awake and fall back to sleep like nobody's business. If his diaper was dry when I went to change him (started around 8 months, with the first *hints* of bladder control)I'd wake him up a little more, ask him to pee, and then touch VERY gently on his distended bladder. He would, I'd change him, and *poof* back to dreamland.
<grinning> It's fun the things we remember. I'd forgotten all about that until you asked your question. But for a year, every night, I was on pee-patrol as the last thing I did before sleep.
:)
Z.