Like the question says, will a wet mix prevent hose whip? Until I bought the P88, and started reading this stuff, I knew that a boom could whip a hose, but never thought about a line pump doing it.....so?

Yes and no.
If it's a rough mix it won't help, make it wetter and you make it worse.
If it's a good mix it will help some yes.
Confused? I guess so, you just have to look at what you're getting and go from there.

Is a P-88 a ball valve ,if it is my answer is yes if will knock you off a wall when the plug breaks free, I built a rotating wall hook for pumping blockfill and ICF's at corners it turns easy.

Can you post a picture of the wall hook?

Any pump is capable of hose whip,under the right conditions.I would say the ball valve would be the most forgiving of pumps.

Keep in mind there is face pressure on the piston heads.When the blockage occures the hyd pressure builds to max,then releases.As one gets into the larger units (as you plan) the volume/pressure increases.Some of the bigger pumps are rated over 200 yards per hour,that takes a very big seatbelt.

There are candy canes,wall hooks,even for the 4" system.I don't have a pic of one but very handy.My line pump guy uses one to hook in back of mixer for wash out,yes he follows good safety procedures.

Oh,a good safety thought.Never,and I mean never let a driver stand on ladder/step while doing this.Should that whip occure while back washing the results can be horrific.

I am not sure I understand the question, I will assume we are talking about surge. As the others have already said there are many factors, the only way that I know of to reduce the amount of surge is to slow the pump down whether that is backing off the rpm's on the engine or by reducing the strokes by means of a stroke limiter. Unless you are buying the concrete, I would advise against adding water to it, the exception there being if you are completely unable to pump mix without adding water, if that's the case contact person in charge and explain issue to them and have them add water.