Is KTP laser for veins around nose on skin type 4 patients successful?

The skin chromophores targeted by the KTP laser are melanin and oxyhaemoglobin.I agree that RF technology may be better here because it does not target melanin and risk of hypopigmentation is less likely. 

Although your question for facial veins refers specifically to KTP laser, I prefer and use Nd:YAG 1064nm laser. Although both of these treatments can be effective in certain types of facial veins, and can theoretically be used on Fitzpatrick Type IV skin types, I prefer using a device that utilizes RF (radiofrequency) energy rather than a monochromatic single wavelength source of energy (laser). If you view some of the facial vein treatments I've posted on RealSelf, you can see a typical example of the results. Additionally, the results are more immediate (less recovery time), any skin type can be treated with virtually no risk to the darker skin types (NO loss of pigmentation), and risk of burn is absent.