The description of the 4th-level wu jen spell wall of bones [conj] (Complete Arcane 128–9), in part, says, "Though solid, the wall has many small openings and gaps and creatures on either side have cover and concealment against attacks from, the opposite side." So, although it can be bypassed with effort ("Small creatures can slip and wiggle through the wall at will, but a Medium creature" must succeed on an Escape Artist skill check or else be dealt damage by and stuck in the wall of bones effect), the game says the wall of bones effect is, in fact, solid.
The description of the fighter alternative class feature dungeon crasher, in part, says that the creature gains "a special benefit when making a bull rush. If you [i.e. the creature] force an opponent to move into a wall or other solid object, he stops as normal" (Dungeonscape 10).
Because it's described both as solid and as a wall, this DM would have no issue with ruling that a dungeon crasher fighter could, with a successful enough bull rush attempt, dash a foe against a wall of bones effect. Verisimilitude may be strained when the fighter crushes a cat, songbird, or squirrel against the wall of bones effect, but, then again, knocking enemies into walls is this fantasy warrior's jam—being talented enough at bull rushing so as to aim a little foe at the wall of bones effect's more solid parts should come with the territory.