I am low carb and have been for 3 years. (currently around 30g) I have never taken a supplement in my life because I have absolutely no deficiency symptoms. I believe if you are deficient in some vitamin or mineral your body will tell you and you will have symptoms.
After reading on here about others taking supplements I was curious so when my last HbA1c was due I asked for extra tests for Vit D, Vit B12, and Folic/folate. My GP also threw in ferritin and iron tests for good measure. They all came back well within standard.
If you are on Metformin you need to keep an eye on B12 as Metformin tends to disrupt this vitamin.