If it was up to me, I think he is less skilled than the others compared to Gin and Vermouth who are high ranking members and are known for their superb skills. But Vodka on his own as a character with no comparison, like mentioned, have an almost accurate shooting skills, can remember faces and names, useful in handing out a trade. seems to have no conscious as he is prepared to kill anyone anytime except maybe for Gin his mentor, a trait that earns him respect I presume. Vodka perhaps is more of the business dealer kind of man, as Gin would probably kill on any little doubt thus Vodka is assigned to work with Gin to smooth up the deals therefore in the very first episode he is the one to trade with the arms dealing company leader while Gin is on the lookout. Wow it just hit me but if you think about it for a second and that Gin is more of the combatant between the two, have you ever thought that Gin is assigned to work with Vodka as the bodyguard and not the other way around. Vodka is the one to deal with others, but since he have less of a charisma and leader skills and intimidation about him, Anokata assigned Gin to work with Vodka to assure that Gin would handle any situation that Vodka may fall into and that is why they are together. True Gin would not hesitate to kill Vodka as seen before, but perhaps Vodka has some kind of relationship with Anokata but at a disposable range. That is why Gin is the one who is with direct contact to Anokata because he can handle any situation at hand, while Vodka assuming he is more close to the boss is kept at hand so that his dim witted mind will not be a problem.
Remember that even though Pisco was a long time member of BO and was somewhat close to the Miyano's, he was disposed off immediately at the risk of covering the existence of the BO. So Vodka might be in the same situation, if he is also close but due to his slow mind kept at bay to ensure his incapability won't risk the hidden existence of the BO.