I haven't seen your weedy oaks, so its tough to make a good recommendation.
I have bought some weird tools or made them, for site clearing.
The most bullet proof grapple I have is the Gregory Grapple. It might have too great of spacing between the tines for your application. But it can do many different things, and is far more versatile than any other tool that have.
A land clearing rake can do good in brushy stuff, and mine is made by Attachments International, it is really tough, and does well in thinner stuff, and for backdrag raking. It is so durable, to unload it sometimes I just tilt my dump trailer and dump it out! It is like an Anbo brand rake. The Anbo has a better shape than mine, on the bottom of the tines for engaging the surface, moving forward. Remember with these rakes, that skid steers aren't bulldozers. They don't have a lot of tractive force unless you have a track model or over the tire tracks. Also, short wheelbase machines on tires are tough to rake with on uneven surfaces. They bob up and down and gouge the surface easily.
For small trees, I made a grapple that picks everything vertical, like fenceposts. For lack of a better description, it looks like giant Vise Grip. It pinches to zero at the tip, and the middle has a greater opening for fence posts on the end, or small trees. This is a neat tool, because it capitalizes on the loader's lifting ability, and its precision. There are other commercial grapples that have come out since then, but something like this isn't too tough to make. There is one good one, for sale but right now I can't recall its name. I think its made in Texas called Brushstar or something like that. It was made for mesquite brush.
You can check out many tools online, and most will also send you demo DVD/CDs so you can check them out if there isn't a dealer near you.
Buyer beware though, there are some cheap units on Ebay, or sitting in auction yards that bend easily. They either suffer from poor materials or workmanship. If they did not start with a suitable piece of metal no amount of welding artistry, painting or stickers, is gonna make it a durable, tough, site clearing tool.
Price point can be a good indicator of quality.
.02 A.G.