Most likely what is being reported are the effects of last spring's late freeze. This was particularly damaging to Japanese maples across a large part of the Northeast, as the trees were just emerging from dormancy when the freeze hit.

Because they have rather thin bark, Japanese maples can easily suffer from bark scald or freeze/thaw effects and in colder climates, it may be prudent to take precautions for this. The bark is also appealing to squirrels, who strip it to use for nesting material. This is a pretty common occurrence here in late spring.

Once the bark is split, there is little you can do to correct it. If the tree is otherwise healthy, it will compartmentalize the damage and scar over.

Thanks for responding gardengal. I'm hoping it'll be alright. I'm just worried that when the freeze/thaw starts again this winter and I've got that weakened area, I don't want it to break off right there at the graft.

I sure wish there was something I could do.