The catch -- the salvage missile which has to combine total resistance to ECM, hacking tools to "break into" the derelict ship's computer systems, and at least a partial guidance/docking computer...now costs 3000 credits at a main station and a whopping 4500 credits at the Dredger itself.
Boas, Boa 2's, and Anacondas are rare as derelicts because in the plain game they're NEVER pirates and only rarely become offenders via friendly fire incidents.
Adders are never pirates either, but they also have zero chance of an escape pod. Many of the smaller ships cannot normally be salvaged unless an OXP adds a version of them with an escape pod.
My big problem with Dredgers OXP is sometimes the salvage ship misses its rendezvous with the dredger because the dredger semi-quickly moved at a right angle with the salvage ship's flight path...and seems to end up too far away from the salvage ship's stopping point for the ship to locate it.
Ironically, I have found when this happens that I can get very near and/or bump the salvage ship at dead slow speed (causing effectively no damage to it or my ship) and the salvage ship "wakes up" from its dead stop and proceeds to dock with whatever station is nearby. I've seen many dock with Rock Hermits as a result...and a few plow into Rock Hermits at full speed as well.
I will see if I can improve its ai, because after the long delay...watching an expensive Python crash into a Rock Hermit is a real letdown.
My advice for attempting to salvage ships is disable everything along the trade route, kill all obvious pirates on the trade route...or just wait 10+ minutes for average traders and Vipers to do that, then go to main station, empty cargo bays, buy salvage missile/s as needed, save game, THEN go out and attempt the salvage mission. There's a fair chance you can also salvage one of the pirates you'll encounter along the way to the dredger...so carrying 1 extra salvage missile can often pay off without having the long travel delay twice.
If you see a group of derelict ships parked along the trade route, go for the Anacondas, Boa 2s, Boas, Pythons, and then Cobra 3's in that order to maximize profits with minimal number of salvage missiles. If done quickly enough, you'll only have to fight pirates along the way for the first one.