Simply, the answer is no.
Vitamin C drops in the water degrade too rapidly to do any good. Once the light hits the water bottle the C starts degrading and within a very short period of time, the C is already gone. Also the drops can distort the taste of the water making pigs drink much less.
Tang should NEVER EVER be put into a pigs water bottle. Tang contains refined sugars, very little vitamin C and dyes.