To align the derailleur hanger you don't need any special tools. At least with steel frames, the derailleur hangers can usually be bent without damaging them. Basically you have to do two things:
- Check the derailleur hanger alignment
- Bend the thing carefully until it is parallel with the wheel
For (1) you can use a spare rear wheel with a threaded axle. The axle threads are the same as the threads in the derailleur eye. Remove the derailleur and screw in the wheel instead. Use a spanner to tighten it a bit, so that the cone sits square against the derailleur hanger. With the now two wheels in place, you can measure the distance between the rims in several places. If the derailleur eye is straight, you should get (approximately) the same distance everywhere. If not, it will vary and you should be able to see in which direction the hanger needs to be bent.
For step (2), bending the hanger, you can use a large adjustable spanner. Align the spanner in the direction you want to bend the hanger and tighten it so that it holds the hanger well. Then bend carefully, preferably in the section between eye and dropout (and not at the "U-turn" of the dropout). I usually leave the back wheel in the dropouts and tighten the quick release, in order to give the dropout some support.
Bend a little, then check the alignment again and repeat if necessary. When done, carefully check dropout and hanger for any cracks! As said, steel usually survives quite a lot, but you don't want to risk losing your wheel because of a dropout failure.