OP, Proserpina has dispensed some excellent information.
So, I will only add that IF your "ex" does eventually get disability benefits, you likely will get paid.
But, it might be a drastically reduced amount.
Why, do I say that?
Well, social security (SSI) payments are often untouchable, as far as child support goes.
This excerpt from a well written article explains it well.
Even if he were to receive SS payments, his obligation would likely be adjusted downward.
Either way, this would be considered a significant change in circumstances.
By the way, this article was written by a Michigan attorney.
1) The child support may go DOWN but it's not going to go away
Ok, let's get it poppin! Under Family Law for most states, a person who is required to pay child support may be able to petition the court to reduce their child support obligation based on a material change in circumstances. In other words, if their obligation to pay was based on a certain financial calculation at the time they were working, they may be able to lower their payment if certain circumstances arises that prevents that from being able to pay that amount. I'm pretty sure a disability determination by a Federal agency may be helpful. HOWEVER, just because you're on disability doesn't mean that you NO LONGER have to pay child support. The clock still runs and as long as you're receiving benefits, you are still on the hook to satisfy your obligation. It may be lower but you still have to pay.
2) DIB may be garnished
When you worked and paid into the system, you earned quarters of coverage which allows the Federal Government to pay you based on your earnings. As a result, if you are on disability, you may be able to draw money per month based on your earnings. As a result, most state Department of Revenues have relationships with the Social Security Administration which permits them the ability to garnish a percentage of your disability to satisfy your child support obligation.
3) SSI might not
Most people don't understand that Supplemental Security Income is a NEED BASED program (in other words, a welfare program). As a result, when you apply, you usually a) don't have enough quarters of coverage from your own earnings, b) are disabled, and c) are so poor that you need the monetary assistance to survive. In some instances, child support agencies may not be able to get at disability benefits because this program is need based.
5) You gotta be ON disability in order to get it done
People think that as long as they are APPLYING for Social Security Disability benefits that they don't have to pay their child support. First, this almost never works because most judges aren't moved by an application for Social Security or a letter from your representatives saying that are applying (some judges are sympathetic. Be happy if you got one). Second, until you have a determination from SSA that says you are disabled, the courts may not be sympathetic until you get a decision. Finally, the decision takes so long that the family court is not going to sit there and wait for you to be approved or denied.
6) The Family allowance is not to cover your child support debt (DIB)
Under the DIB program, if you have kids, you may receive an additional amount of money for your children. However, this extra amount of money is not amount to satisfy your child support debt. Sometimes, people think that this extra money goes towards that obligation. One, the extra money goes where your child is. Two, the extra money is NOT designed to cover your support obligation. Three, you are STILL responsible for child support.
7) You have no choice. The Government will take your money if you owe child support.
If you are on the DIB program, the State will garnish a percentage of your money. I hate to be the bearer of bad news but you have NO say so in the matter. You can appeal and tell them that you need to lower the percentage (good luck with that) but the reality is that states and the federal government have a relationship to ensure that you satisfy the obligation.
Child Support and Social Security can sometimes work funny with each other. However, the reality is that the Child Support obligation doesn't go away just because the person is on disability. However, SSI programs are for those people who really NEED money because they are financially destitute so there is no guarantee that those funds may be garnished. Disability may not exempt you from your obligation, however, the program you fall under may impact the child's ability to receive it.
http://legalbeat.anthonyreeves.com/.../child-support-and-social-security-disability