I've given up on wanting to deal with the stress of difficult bonds. It's just not worth the stress to me or watching the rabbits being stressed, but that's just me. I'll only do love at first sight bonds now, so maybe I'm not the best one to comment. I wouldn't bother with a difficult bond like this, but I know some people are willing to go through the effort it takes.
It doesn't look totally unpromising, as he's not all out attacking her. To me it just looks like he's trying to chase her away from what he thinks is his space. So it's possible he could eventually settle down and be ok with her being around. As long as she doesn't get fed up and start fighting back. Then I could see an all out attack occurring, so you'll want to carefully monitor that possibility as it could turn brutal.
Grooming is a good sign. The problem I can see is that you are doing it outside, and once you start you shouldn't stop, but being outside you will have to stay outside to accomplish that. If you change the location of their area, or stop tonight and start up again tomorrow, the chasing and biting will likely start up again. The fast method, you want to keep the area the same and not stop once you start(which can mean a sleepless night or more). And even once the rabbits are getting along, you often need to leave them in this area for several days to possibly weeks, before you are able to move them to their new space, and then you may not be able to just put them in their shared area as it is, but you may have to restrict the space to a smaller area and gradually expand, as some rabbits will start to have problems if the space is expanded too quickly. The other problem you might be having is the bonding area is probably too big.
Though some rabbits need a lot of space to learn to like each other, more often it seems that a small space is needed and what is usually used to fast bond rabbits. And that is usually only like a 2 ft x 2 ft square space. Too large a space can lead to increased territorial behavior and the chasing and fighting you are seeing. It can also lead to avoidance and trying to stay away from each other. You want the rabbits to have to be close enough that they have to learn to get to know each other and not just avoid the other rabbit. And you don't want so much space that one of the rabbits thinks it has to defend it's space. Once they are getting along, then usually the bonding space can gradually be expanded a little at a time.
Now a smaller space isn't always the best method, but because of your rabbit reacting the way he is by trying to defend his territory, a smaller space is certainly something that I would consider trying out.