Yes, very much so! An overdose of vitamins can be very harmful. Especially try not to ingest excessive amounts of fat soluble vitamins, A, D, E and K.
As for B6, it is found in: "most foods, esp. whole-grain cereals, wheat germ, bananas, potatoes, beans, liver, poultry, meat; also made by gut bacteria"- Student Handbook, Vol 5. 1998, and deficiency symptoms include: "skin problems, cracked lips, anemia, weakness, irritability, depression."
Since B vitamins are water soluble, taking a supplement of B vitamins shouldn't be any kind of problem. You could also just take a multi, as they have the B vitamins included. DISCLAIMER: I am not a doctor, blah, blah, consult and doctor, blah.
I am pro ditching the Atkins though. The only way to lose weight is to reduce caloric intake or burn more calories. Anything else is water weight and snake oil, to my way of thinking.