Don't know about long-term graft compatibility, but sylvatica can be successfully grafted onto gradifolia. The JC Raulston Arboretum, for instance, offered a couple of cultivars, so grafted, a few years back to select new wealthy members of their Friends of JC Raulston Arboretum Society.

Here is a link that might be useful: See about 2/5 down the page.