Okay, so, this is probably going to be the most amazing thing if this is true. Okay, so, lets look at the trailer, even though it is very unreliable because they are twisting things around to make it different then it turns out to be, but lets just use it for curious purposes.
So, several things, about the preview. Hank is pointing his gun at something in the bushes. Less than as soon as we see that, Monroe erupts out of the bushes, and knocks him over. The one curious aspect, Monroe is morphed in his Blutbad form. Strange. Then of coruse, we have Monroe talking to Nick, saying, "I ran into Hank the other day." After that quote, is Nick yelling (probably in amaznet) "He (Hank) saw you as a Blutbad!?"
Okay, so, this doesn't mean he's a Grimm. Monroe could have morphed in a way for a human to see. The dialouge from the preview seems like Monroe is saying "He's a Grimm." Previews are very sneeky, but if Hank is a Grimm, it will change everything. That would help Hank explain these strange homocides, like the one in Template:Ep and Template:Ep. All in all, it would be so insane for Hank to be a Grimm. Now, if there are two Grimms, both friends and cops, they'll probably learn from each other, but... Aw, forget it. Let's just wait and see.
Put your thoughts down below and feel free to critisize and scrutinize.