If you use the right technique, you can use a pump to improve EQ. Alternating the vacuum up and down (pulsating) is one. Read through some of the articles on pumping. Avocet8's routine for pumping with ED is another EQ improving technique.
Several members will disagree, but I feel pumping on its own will not generate cemented gains. Some great short term temporary (hours) gains and possibly some mid term (weeks) gains, but in my opinion if you stop, they will all dissipate.
Pumping is a great complement to other exercises. I personally combine pumping with extending (before and after), hanging (after), and clamping, (before and after). I'm not a big jelqer, but I can see where it would help before and after.