I agree with the general idea that vitamin supplements really will not add much to your health, nor your hairloss in specific.. But!.. this only applies if you eat a healthy diet with ample servings of fruits and vegetables each day. If you eat a good diet, chances are you are getting the nutrients you need.
However, I very strongly believe that there are certain vitamins that we should supplement ourselves with, the B complex in particular. These vitamins are water soluble and are not absorbed and stored in our bodies like the others are. This means that B vitamins, when ingested, are not stored in the system for future release on days when you do NOT ingest ample amounts of B vitamins. Basically, you eat a meal with good B vitamin content (say, tuna fish) and by the end of the day you piss it all out and the following day your body is lacking in them.
Keeping in mind that B vitamins are essential for optimal metabolism, and are great for the skin, I think it is important to keep on top of this.