Does cortisporin (neomycin polymyxin and hydrocortisone) cream help poison ivy?

Probably so. Cortisporin (neomycin polymyxin and hydrocortisone) is a combination of a steroid and a topical antibiotic. The steroid is probably the component that is doing the most for your reaction. I would avoid the topical antibiotic unless there is truly a bacterial infection that needs to be treated. The antibiotic portion carries the risk of an allergic reaction and can confound the clinical picture.