Under no circumstances whatsoever would I even consider contributing to someone who is going to serve time for a 3rd DUI conviction. For people who drink and then get behind the wheel and drive, that car is a weapon that kills as surely as any gun... and the person they kill is just as dead. Some people just don't get it until a drunk driver kills someone they love.
If you want to help Mom, talk to her about going to an Alanon meeting because she sounds like she is an enabler... most enablers are wonderful, sweet people who just don't/can't understand that their actions actually "enable" the kind of behavior they want to stop... i.e. drinking and driving. He'll have no incentive to change if she is constantly trying to "absorb" the pain for him... incarceration, no soap, no socks. Well, yeah, that's what happens when you have a 3rd DUI conviction. Mail him some socks and a bar of Ivory if you really can't resist.
Do I have compassion? You bet I do... for all those sons, daughters, mothers, fathers. friends, etc. that drunks have murdered on the road. For some people, it has to be THEIR son or daughter before the reality of it makes an impact.
Thank God this man hasn't killed anyone... yet. How would Mom feel if it was you, DH or one of her own grandchildren who ultimately became his victim?