In Indiana, does a parent getting a lump sum Social Security disability payment entitled to a credit against the parent's child support obligations?
The answer is: Yes.
From the Indiana Supreme Court opinion in Brown v. Brown (which is in PDF format):
Because of Danny Brown's disability, his son received a lump-sum distribution of retroactive Social Security disability benefits as well as monthly benefits going forward. Brown seeks credit for the lump-sum payment against an accumulated child support arrearage and credit for the monthly benefits against his future support obligation. Following precedent from this State and others, we hold that a disabled parent is entitled to credit against the parent's child support obligations for Social Security disability benefits paid to a child, effective as of the date the parent files a petition to modify a support order. The petition may be filed upon application for disability benefits.