I've been grafting oaks for 25+ yrs. Almost as easy to do and as successful as apples. Certainly much easier than pecan/hickory/walnut.
I've not kept up with time to bearing, but as is the case for grafted selections in other species, I'd anticipate time to bearing to be cut in half or less than the time you'd have to wait for a seedling to grow through its juvenile phase and begin masting.
A simple bark graft, done with dormant-collected scionwood, just as the rootstocks are beginning to push leaves, works well. Other techniques probably work, too, but this is how my mentors, Mark Coggeshall and Fred Blankenship, taught me how to graft them.
I've grafted small 1-yr old potted seedlings, and topworked established trees, up to 3 inches dbh. Those established trees will push as much as 4+ ft of growth in the first year.
Graft compatibility across the entire white oak group appears to be good. Red/black oak can have some peroxidase enzyme incompatibilities that will result in graft failure.
I use mostly bur oak as an understock for any species or hybrid in the white oak group, as that's what I concentrated on early in my plantings, so have plenty of acorns & seedlings to work with - plus, they grow very fast, and are adaptable to a wide range of soil types & pH. Large-acorn type bur oaks push a very vigorous seedling. I'd probably avoid post oak as an understock, as it's so slow-growing.
I have a couple of NuttallXPin hybrid selections that I've topworked onto various red/black oak understocks - Northern Red, Southern Red, Pin. Northern Red and Southern Red look like they're going to be compatible, long-term, but the ones on Pin oak have a funky-looking graft union, even 10 years out, that makes me think that they're gonna fail at some point... may just break off right at the graft union in a wind event.
Now, for a caveat... In some of my original plantings, I had some BurEnglish oak seedlings, purchased from OIKOS Tree Crops, back around 1996... real 'mongrels', if you will, 'cause they were open-pollenated seedlings of a putative BurXEnglish selection Ken had made with any of the species and hybrids in his orchard potentially serving as pollen parent. I topworked them to the 'McDaniel' BurEnglish selection, made by J.C. McDaniel (UofIL) from a cemetery somewhere in IL. They have grown and produced well (see attached photo of acorns) for over 20 years, but in the last 3 years, 3 of the 5 grafted 'McDaniel' trees alongside my driveway have begun rapid decline - lots of dead wood in the canopy, many epicormic sprouts from the rootstock below the graft union. I removed one tree this spring, that was all but dead, and another one will probably be removed this fall, as it's fading fast, and looks as though it won't produce any acorns. One more is looking like it's starting the downward spiral, but the last two look to be OK, for now.
Other bur oak and hybrid oak selections, grafted on BurEnglish rootstock from that same batch of purchased seedlings , look to be unaffected.
