In The Clone Wars, is Jango Fett still Jaster Mereel's protégé /adopted son?

Short Answer: Most likely, yes, but with a few changes.

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Long Answer:

I'm not up to speed on The Clone Wars show, but the history you've quoted from it definitely conflicts with what we knew prior to the show. In Jango Fett: Open Seasons, it is clearly explained that the Mandalorians IN GENERAL are split into two factions - the True Mandalorians led by Jaster Mereel and the Death Watch led by Vizla. There was no mention of the third faction, and Jaster's faction were definitely NOT pacifists. In fact, the primary difference between the two was simply a matter of honor - Jaster liked to pick & choose the jobs his people took, whereas the Death Watch would take any job, even resorting to piracy and genocide if needed. Keep in mind the quote you used is from a wiki, so that may just be a fan lumping Satine and Jaster together incorrectly.

Here's what we knew before the show. During an ambush by the Death Watch, (possible spoilers)

A young Jango's family is killed by the Death Watch during one of the early skirmishes between them and Jaster's True Mandalorian faction. A vengeful Jango then showed tremendous spirit & skill facing the Death Watch members. Impressed with the boy, Jaster adopts him as his son/protege and raises him. Years later on a mission, Jaster is killed on the battlefield and Jango assumes his mantle of
leadership. Jango then leads the True Mandalorians for several years
until the Battle of Galidran, which sees the last united group of Mandalorians wiped out.

For the next 30 years, until Boba Fett later unites them again during the Yuuzhan Vong invasion, the Mandalorians are a scattered and nearly extinct people with no leadership. Now, obviously, this doesn't jive with The Clone Wars and its concept of a peaceful, united Mandalorian society back on the homeworld.

However, any time there's a conflict between EU material and a Lucas source, the Lucas source wins by default. So in this case, the events of The Clone Wars would seem to now be the "official" history of the Mandalorian people. sigh.

However, to more directly answer your question, there are some references in episodes of The Clone Wars which infer that Jango/Boba is still considered the adopted son/successor of Jaster Mereel, at least in spirit if not political role.

From what I've been able to glean so far, one of the few references to Jaster in The Clone Wars was made in regards to the armor previously worn by Jango Fett. It therefore stands to reason that most (if not all) of the previous continuity might be retained. After all, if the armor worn by Jango still originated with Jaster, then maybe we can fit in the rest with a little massaging & lube. It also appears that the New Mandalorian faction rose to prominence AFTER the events of Open Seasons, which could conceivably allow the two continuities to co-exist with only minor tweaking.

For example, the leader of the Death Watch - Pre Vizla - could be a relative of the Tor Vizla featured in Open Seasons. It's possible that he united the remnants of the Death Watch after the events of Open Seasons. Considering the new EU policy under Disney, it's really up in the air for now. Both Boba Fett and the Mandalorian people in general are set to be featured heavily in the new show "Rebels" so maybe it will be addressed there.