Fun user name and avatar, Commander.
As you’ve probably read, vacuum pumping is used as one means of decreasing the degree of ED. Since the preponderance of ED is caused by vascular problems (about 45 percent of ED cases) and pumping tends to increase vascular efficiency by keeping veins and arteries 1) clean of fibrous buildup and 2) increasing the delivery capacity of newly oxygenated blood, it would make sense that over time you would probably see more vascular prominence on your shaft. Shorter but repeated pumps sessions (6 - 8 min. each) probably increase this development faster than long periods spent in the tube in one session because you are repeatedly pumping up, then deflating, then pumping up again.
Before I started pumping going on five years ago, I had one noticeable artery, the main dorsal one, that sort of stood out and that only showed during erections. The rest of the shaft on both sides was smooth. Now though, there are veins and arteries branching and criss-crossing every which way and several main “feeders” instead of just one. They are prominent whether hard or flaccid but much more prominent erect.
When some new ones grew in the last year that are even more distended, I asked my urologist, thinking I had thrombosed something but he said, no, that I just have a very efficient penile vascular system and why worry if erections happen faster and last longer?
I think some of the vein growth you are talking about comes with size gain. If you increase penile volume, girth and length, and your cavernosal chambers enlarge, your blood delivery system has to change somehow to accomodate the larger size for erections.
The look of this is kind of “mean” :) and I like it a lot better than when I was smooth.
Since in more than a year I have done minimal jelking and mostly pumping, I have to conclude that the pumping influences vein growth more than jelking does.