Saw an update to you post, and after thinking about it, thought I remembered something that may be your perfect tool. That was until I saw you needed to uncover the graft union, shows what I know about growing grapes. Don't know that I've seen that done here in Ohio with all of the small Vinyard/wineries popping up all over here. It may very well still work for you, if you could find one. They are known as terrace makers, a pull type PTO driven type plow that slings dirt to make terraces on hillsides. They had a 3 speed transmission so as to sling dirt further. I'm thinking in first gear at low rpm's, and running just shallow enough depth to get the amount of dirt to do the deed. In this video, this one is powered by a Farmall H, which were 28hp on a good day. As if you don't have enough wheels turning inside your head on perfecting your build, I'm going to throw this at you.
Now that I see you need to uncover the vines at the graft union I'm wondering if some sort of compost would do the job for you. It would be something that would take several years to produce using an organic material such as leaves, straw, etc. to semi-break down into something usable. Not completely composted, but enough it may break down over the winter, and settle come spring and not so difficult to pull away from the vines. It could be applied with a PTO manure spreader with the beaters removed, and a slanted side chute to deposit where needed. I'm assuming the dirt needs to be pulled away from the vine union to prevent rot or freeze damage. And don't have a clue as to how long the semi-composted material would last in your climate for the protection you need. It may not even hold enough moisture if rotting that graft union is the problem. And last of all looking at the pictures I'm not seeing very many trees leaves could be harvested from. Here for most people that have a lot of trees they are a nuisance and either rake/blow their leaves up in a pile and dispose of by whatever means to keep from smothering the lawn grass. Others have lawn services blow them in piles then have a truck mounted Vac to pick them up and dispose of. There are several composting facilities around but charge a hefty price to dump.
In my case I've been mulching around set plants in the garden now for 10+ years. Keeps the weeds down plus after breaking down adds a lot of organic material to the dirt. I gather from neighbors, and in the past had a neighbor with a lawn service bring me huge amounts. Worked great until the guy's wife who has a small CSA saw what I was doing, and decided she would do that, and there went my huge leaf supply. By luck a buddy of mine was helping out a friend of his with a lawn service who provides leaf pickup. The city where they normally take them that has a composing program upped the price to $50 to dump a 1 ton truck with box. It was either cut the profit margin, raise prices, or find a less expensive place to dump. My buddy remembered I mulch with leaves, so called and asked if I wanted them. I told him "all you got." I ended up with quite a pile and hopefully enough to cover the entire approx. 1/4 acre garden.
By spring they'll still be pretty much whole. I'll put them around plants after they get 8" or so tall. Once they are down they will suppress 95% of all weeds all summer, plus holds moisture through dry spells and sure saves a lot of work. I put them down 4" - 6" thick, by the following spring they are pretty well broken down into a fine compost like material. Over the summer they provide a mat to walk on after a good rain, yet the following spring plow down very nice. Earthworms and night crawlers feed on them from underneath the entire year and leave untold amounts of worm castings. A pretty cheap source of organic matter, plus organic fertilizer.
Below is a picture of some of the leaves I've gotten this fall. There have been several more loads dumped since then. Looking at your pictures the population looks pretty sparse, but pictures can be deceiving. Not sure if this will work for you but throwing it out there as food for thought. Also added a picture from early August and how well leaves kept the weeds down. I give and donate a lot of tomatoes once I get what I want for canning and get many complements from people on how nice it is to pick in a weed free tomato patch.
