Depends on what you mean by 'matte spray'--there's fixatives used for drawings, but usually the varnish on oils is applied by brush (unless there's some new prodect I'm not aware of).
Are you thinking to use something like Testor's Dullcoat over something you've painted in oils on a figure? If so, I don't have any advice on that, though I have heard of people using Dullcoat over acrylics. I don't know about using something like this over oils. You might want to experiment first.
If you want to dull down your oils (make them 'matte'), use Dorland's Wax. It's specifically designed for that purpose.
--Linda
