Can someone sill be arrested for back child support if they are unemployed?

Pretty much anyone can be ARRESTED any time a cop feels there is probable cause.  Your question really appears to ask whether a person can be charged with non-support and convicted of criminal contempt (or perhaps civil contempt -- they are different) if unemployed.  The answer is "maybe."  Nevada case law does support the "impossibility" defense, but the cases are pretty harsh and lean toward the obligor making every conceivable effort to comply with support orders.  If there is such an order, and you cannot satisfy it, the smarter thing to do would be to file a motion to have the support owing reduced due to your unemployment.  See http://willicklawgroup.com/child-support/.