My wife was prescibed voltaren (diclofenac) 100mg. She breastfeeds, so will this be a problem? Does "pumping and dumping" work to get voltaren (diclofenac) out after 8hrs?

No. This medicine is not safe for use while breastfeeding. I would recommend not using it at all and getting an alternative med from your doctor.
Check w pediatrician. Probably not, but always check w kids doc. In general, don't use meds that are not clearly indicated. Yes, many drugs will cross over to the breast milk. Remember, the drug is cleared within 24 hours, but when you pump your breast is what's in it, not when you dump it. Any reason using voltaren (diclofenac) and not some other nsaid?