Let's say either a stationary particle of matter, a photon traveling in the opposite direction to the vehicle, or a photon traveling in the same direction as the vehicle. Would they ultimately end up inside the bubble to encounter the vehicle traveling within?
This ArXiv pre-print by Brendan McMonigal actually answers this problem! He considers particles of velocities ranging from $-c$ to $+c$ (the sign denoting direction relative to the bubble, I believe) and finds that, for the most part, the particles would indeed enter & exit the bubble (receiving a velocity boost) without much trouble.
The trouble, however, is that this particles can damage the shuttle and passengers within the bubble!