1.) To vote is to consent to be governed by the victor.
2.) Government operates via the use of violence-&-force.
3.) If the victor uses violence they were empowered by your vote.

Q: Can the violence be violence, if one volunteered themselves to be subjected to it via their vote? Or is it a contract being fulfilled?

See: Consent of the governed
Keywords: when consented to by the people or society

I'm just thinking aloud here; I think the question is complex, and could be viewed in more ways than one. If government were to refuse to act forcibly upon those who did not participate in the voting process, then voting wouldn't be violence, because everyone subjecting themselves to the violence of government would have been a willing participant.

However, our government will immorally wage violence against people, regardless of their participation in the vote. This tends to puts some folks in a desperate position wherein they will vote as a plea for mercy.

If a woman were about to be raped, and knew she was going to be raped, and begged the rapist to wear a condom. By doing so, is she consenting to sex? Or just trying to avoid some of the potential consequences that might result from the rape?

When considering whether or not voting is violence, you have to consider the fact that government has many people in a state of Stockholm syndrome. That makes answering that question far less cut and dry.