I expect this to lead up to Gordon taking over for Sanji for good. Especially with the Baroque Works arc coming up.

Yeah, same thought just crossed my mind; DM will eventually take over GMing, and Gordon will start playing Sanji full time.

This could explain why she is only named DM.

It would also explain other actions, though again I'm expecting DM's actions will make her not liked by the group and she will get pulled back in as Robin(after playing robin as a pet npc well she gm's the game)

Hmm...no. i agree on the fact that the group save for Luke and maybe Rika, might end up warry of her (Cory already is), and i also think she will be playing Robin, but i don't think so about the pet GMPC part.
i don't know, DM play like a jerk, but she does'nt seem like the kind of "i create a pet NPC" jerk.
For exemple, there was someone i knew who would act egotistical and put the other's pc in danger to save her own (she was a nice person outside the game, but her playstyle could get annoying for us), but on the other hand, she was the first one to opose stuff like GM boy/girlfriend privilèges. what i mean is, there are different kind of jerks.

My guess is that Robin will be introduced as a straight-up antagonist for the Alabasta arc (she was part of baroque work, remember). but in the end, Luffy (Luke) decide "nah, i'm saving her" and his the one to invite DM to use her as her PC (like he insisted on gordon playing Sanji Ramsey). The others are like "What the hell, luke?!" and she convince them that she ain't planing to backstab anyone this time. Zoro is stil Warry of her at first because Cory know DM and think there's still a risk for her to betray them.

I dunno, actually. Sanji spent a lot of time in the Baroque Works arc out of sight, then showing up and saving the day.

My guess is that DM will be DMing at alabasta. which explain why Luffy get down two or thre time before managing to beat crocodile. And Sanji get a one on one fight.
Before that, i'd say it's still gordon the GM, which explain why Sanji is the one to stay out of the action in little garden and providing the crew with a solution when they think they're stuck in the island.

I thought she was called DM because she used to be their DM.

Those are her initials. One Q+A mentioned what they were but I forgot.

DM are her initial, and it happen to fit with the fact that she was their DM, so that's her nickname.
the Q&A revelead that she was named Dellila, but we don't know what the M stand for.

GM is named Gordon and hes playing Sanji. I find this funny proceed.

Does it require anything special in Pathfinder to bite someone who is right in front of you?

Really asking; I know I sound like a broken record, but I'm not familiar with the system (played some D&D 3e over a decade ago =P). The systems I have played do allow people to try a bite, it is just usually its a really stupid way for a human to attack (low damage, risk of injury).

However sometimes grappling makes normally difficult targets much easier. For example, if two humans are grappling face to face, the usual -3 penalty to hit the groin doesn't apply to a knee strike.

honestly, if he don't let slide a little, they're dealt with. And gordon is the kind of GM who like to keep the game going.
i can understand that. the GM once saved my friend character because "Hey, i haven't written all that plot for nothing and i need youc PCs alive for it."

I wanted the next arc to be tied to his PC's backstory.