Theoretically there are ways to "iron out" dents in tubing. A mandrel with tapered ends is slid into the tube and force through it either mechanically or hydraulically, raising the dent in the process. This is done often with dented shotgun barrels which are much thicker walled than any bike tubing.

However (and this is a BIG however), you have to be able to access both ends of the tubing. It might be possible to raise a dent in a seat tube but any others are probably inaccessable.