With respect to correcting homework, I think here it does matter a lot whether the problem is actually LD-based. It can be really, really hard to judge, but I try to think in terms of what the child could reasonably be supposed to do, and what they have been explicitly taught to do.
I tend to bring two considerations to this. First, if the child couldn't reasonably be expected to spell without an O-G based spelling program, I don't correct any spelling that involves words forms that have not yet been explicitly taught. Besides feeling like punishment, the reality is the child probably isn't going to learn anything from your corrections anyways if they are not within the context of a structured program and rules the child has already been explicitly and systematically taught. (My DD is highly motivated to spell my name correctly. She's seen it written correctly a million times. She still spells it differently every time.)
Second, what is the purpose of the assignment? Is writing the end, or a means to the end? In the latter case, I think it's important to be way more hands-off than the former. LDs are a lack of automaticity. That means the child needs to expend enormous brainpower on basic mechanics of spelling, letter formation, location of letters in space, etc. While they are doing this, there's not much brain left for anything else. So in every assignment, I kind of have to consider: where do I want the majority of her brain resources spent - on the mechanics, or thinking about the content? Because unlike the other kids, she has to pick one. So it's good to have stuff that's all about practicing the mechanics - and the rest of the time, ignore them.
Incentivizing can be very helpful for most kids (not mine, alas, but most). The challenge is to make sure it doesn't inadvertently turn into a punishment - for something the child can't control, or for lacking a skill that has not yet been taught. You also don't want to incentivize the child into thinking only the mechanics matter, and convince them to put no resources into thinking, creating, and analyzing.
My DD is now 11. When she does something for presentation - a poster or a birthday card - she will still check spelling with me on virtually every word, because it matters to her to get it right. But the work then becomes almost entirely about spelling, and content is subordinated. But she's a poet, and when her muse takes her, she runs to her whiteboard (where there's no spell check to distract her), and whips up the most extraordinary, beautiful poems. Barely decipherable poems. When she's done, she recites them to me (because there's no way I could read them) and I type them up for posterity. If she was thinking about spelling or word spacing or anything else, those poems wouldn't exist and my world would be a lot less amazing.
