1) Powered EHOLE visually acts like any solid wall and is drawn over the pressure visualisation. In your save, the EHOLE is initially unpowered, but gets powered in a few frames after unpausing.
2) Yep.
3) DMG is special in that its pressure wave glitches through layers of TTAN (and even walls) when it's in explosion mode (i.e. when something that it thinks it can obliterate comes nearer than 2 pixels). This is indeed glitchy, but it's a minor one that we think doesn't have too much influence, but would require more work for your computers to do correctly than what it's worth. The same is the case with BOMB happily throwing its residual EMBR over walls sometimes.