I doubt Very much it is grafted, just a large trunk chop that has not been cleaned out. That in itself is not a large issue either.
If you ignore the long lanky top, then there can be a nice tree in the base of it. I would love to see the nebari though. You shodu remove the Moss from the trunk as soon as you can, it will keep the bark wet and prone to rot.
There is at least 2 -3 other trees in this one, and before that lower trunk with the Uro is removed, I would like to see a picture from the left hand side please.
From that side it may well give very nice movement from the base up thru the bend and than regrow a new top above it. Need to see the Nebbari as well so get rid of the moss
Large Scars and wounds are call "Uro", and although not traditionally made on Deciduous stock, many people are now realising that in nature, the decid trees actually have deadwood, scars and other damage, so why not include them in our Bonsai?
http://www.bonsaiempire.com/articles/ad ... dent-maple
http://bonsaibark.com/wp-content/upload ... h-uro2.jpg
Lots of other examples around the web too than just these 2 links.
Ken