I think so but I think you would also need the posts meta table as well. I am not sure of all the bells and whistles on MySQL.- Is it possible to only back up posts?
- Can hacks also be in posts-back up?
Yes. The hacks I know of add a column somewhere in the data base or an extra file somewhere. You could compare the old posts table to the new and do the same with posts meta.
Since WordPress is dynamic, building pages on the fly, I really don't know if moving the old posts into the data base would make all of the correct connections.
You could create a different data base and experiment or ask your hosts. It is more of an data base question.