Sure it's possible to be a healthy vegan. When I had been vegan for 2 years (I still am after 4) before I had a COMPLETE metabolic blood test - they looked at all my various vitamin and mineral levels, etc. They were all perfectly normal. I eat a pretty healthy diet, although not as healthy as some others - I eat some white flour, rice, etc. and some whole wheat, brown rice, etc. I eat a fair amount of beans and raw veggies (I can't eat much fruit because I have a bladder disorder which means I can't have much acidic foods.)
Veglife brand (made my Solgar) 100% vegan Spectraveg High Energy multivitamins - lots of all those important vits and mins. plus some blue green algae, etc.
Acidophilus once or twice a day to help with digestion (not needed as a vegan but it helps me)
Flax seed oil and borage oil for essential fatty acids (almost perfect skin - cured my eczema, and great hair)
I take the oils and acidophilus every day but only take the vitamins a few times a week because my diet is great. If it wasn't, I'd take them every day.
There are also vegan prenatal vitamins.
Hope this helps!
Early intervention specialist and parent consultant since 2002.