Tremor Racer and Acres Watchhound

I'm not sure on the rules templating on these two mirrored cards.

I think the ogre is easier to understand and subject to the rules than the hound. Obviously it's immune to pacifism effects. But the question here is, does tapping it down so it cannot be declared as an attacker an "effect"? Should it be?

The hound is even more complicated. Not only is it immune to pacifism effects itself, but does this mean it can block creatures with menace or flying or with the green creature ability prohibiting small blockers? Should it?

There is some interesting space for a creature that cannot be stopped from attacking and a creature that can block anything, but it's difficult to write clearly.