The escape attempt (spoilers)

Objectively, the audience doesn't really know. The film doesn't make it clear, and only makes allusions to his possible guilt by the way he puts his head down when Grace returns.

In terms of the film's thematic elements, I don't think it really matters either way. Even if Tom genuinely wanted Grace to escape, he did not prove to be the virtuous ideologue he envisioned himself as, and Grace would have never confronted him even if he was aware of what would happen, because symbolically her role was to forgive all sins.

Tom is symbolic of the intellectual who believes himself superior to others. In the film, he subsists only due to his father, and is never shown working. He views himself as the ultimate arbiter of the town, and through his actions (vying for Grace), ends up having the town destroyed. He is the Quietist, preferring contemplation and passivity over action (e.g., never confronting Grace's rapists).

From one religious standpoint, the town of Dogville is symbolic of the Old Testament. Here, we see people tethered to tradition and bound by principles which limit the extent of human reach (i.e., Ten Commandments). The town is located on a mountain, highly symbolic of Mount Sinai, the place where Moses was given the Ten Commandments by God. The dog, whose name is also Moses, represents the principle maxim of the Old Testament, “an eye for an eye.”

With the appearance of Grace, the town sees the arrival of the New Testament, whose underlying and simplified principle was to turn the other cheek. If the Old Testament sought to punish amorality, the New Testament attempted to forgive sin. Grace, taking on her eponym, and without regard for boundary or transgression, attempts to help the townsfolk. Here, the director outlines his beliefs about the New Testament, indicating that people are unable to moderate themselves independently, invariably succumbing to intemperance. In the presence of grace and kindness, people are unable to control their appetite for more grace and kindness, evolving into extremes.

In the end, we see Grace eschewing the elevation of man and taking "an eye for an eye" to its extreme end. With this, we see photos during the Great Depression, indicating the 20th century death of religion.