Everyone may have a different definition of what "Dirty" Jujitsu is. If it's something being used in the cage that's questionable or against regulations, then sure, lets call it dirty. However, if it's in a real life situation and you were attacked, I don't think their is any such thing as dirty, as the ultimate goal is survival at all costs no matter what fighting form(s) you use.
To me, I think the MOST beneficial art one can include in their training as a 2nd or 3rd mastery is "Pressure points". I watch fights day in & day out & the closest I see to pressure point execution is joint manipulations for a submission win. Learning pressure points would make a fighter almost unstoppable, as even the slighted index finger poke to a spot of the body would send the adversary into a temporary pain & throw their game off long enough for you to land a few cripplers to follow it up. (Ideal for a ground game)
I think the real question would be; Would you consider Pressure points to be unethical or "Dirty" both inside & outside the ring even though it's not stipulated against in the rules, or would you find it to be an asset when used properly?