r_rolo1
King of myself
In short, no. The DP is only a promise they will attack who attacks you, a thing they can't do if they are the agressors 
OTOH normally a civ that is willing to do a DP with you will most likely have enough in the diplo stance to have little odds of choosing you as a target, and the DP diplo modifier will only add to that, but if they are planning to do a attack for a long time ( say, they started looking with greedy eyes to you when they first contacted you via caravel ) or if you are dealing with people that plan attacks at high diplo stances, it might happen. It happened to me atleast twice, both with Saladin ...

OTOH normally a civ that is willing to do a DP with you will most likely have enough in the diplo stance to have little odds of choosing you as a target, and the DP diplo modifier will only add to that, but if they are planning to do a attack for a long time ( say, they started looking with greedy eyes to you when they first contacted you via caravel ) or if you are dealing with people that plan attacks at high diplo stances, it might happen. It happened to me atleast twice, both with Saladin ...