If I give a creature pro black can vault Skirge still be declared as a blocker
This should be in Rules. and the answer is the skirge cant block.
Yea he can block if he's pro black, but he can't be blocked by black creatures. He won't take any damage from black creatures if you pro black him
If the question is if {vault skirge} is considered a black creature, the answer is yes. To determine a card's color, look at its mana cost. If it contains a color (Phyrexian or not), in this case black, the creature is considered that color(s). So, as a black creature, vault skirge cannot block a creature with pro-black.
Normally to clarify with colored artifacts like this, the card has a thin sub-border of its color between the gray artifact background and the card art border. See the green in {birthing pod} for example. But if that color stripe is the same black as the border, like with the skirge...kinda can't see that it has any meaning other than a border.