The main problem, I think, stems from the uniqueness of Jakkard.
Thinking it out, Barinellos's argument has two key points: that we can't say that canon 'walkers have been to M:EM planes [for the chance of being contradicted by Wizards releasing a "this 'walker has only ever been to these planes" statement], and that a 'walker is inherently changed by the planes they visit and that inherently means canon can contradict what a 'walker learns on a M:EM plane.
Now, in response to the first, the key lies in whether Wizards would release any official statement to the order of "this 'walker has only been to these planes." The way I see it, Wizards would only release a statement to that extent for a newly ascended 'walker. While the idea that a 'walker may still be new to the multiverse is likely one we will see sometime, at this point they don't have a large enough backlog of neowalkers to do that any time soon (by which I mean I foresee it taking a number of years over several blocks and expansions before they're likely to do this), and it isn't likely to happen for their older established characters like the main 5 (furry, emo, necro, muscles, and fire) or any of the other big names from the early neowalker establishment. From a marketing standpoint, it makes sense for Wizards to say any walker has visited whatever plane for the purposes of the story/presentation - like how some reprints have the neowalkers' art on them.
The second, that 'walkers are changed by their experiences on planes, lies the issue I mentioned at first. There is a certain amount of wiggle room, I believe, when saying a 'walker (canon or not) visited [x plane]. For each plane, there is a certain amount of "uniqueness," if you'll follow me, that dictates how much of an impact that plane will have on a 'walker. Zendikar on its own was relatively normal; after the Eldrazi were released, it became very unique. Mirrodin on its own was normal; New Phyrexia is unique. If you follow my logic, I'm looking at it from the perspective of how much mortal peril and planar destruction an average planar event (i.e. what we see through the block expansions) creates. Zendikar was perhaps a bit more perilous than an "average" plane, but compared to, say, Innistrad it probably posed the same amount of mortal peril to a visiting 'walker. Now that the Eldrazi are released, they not only represent a plane-wide (and inevitable) destructive event - that in this case has even driven Gideon to go find some sort of solution to the problem - that will eventually pose a problem to the larger multiverse. The same thing can be said about Mirrodin -- the mortal peril was likely the same as on any other given plane until it became New Phyrexia, and Phyrexia poses as much or more a problem to the multiverse than the Eldrazi.
Now, the reason I make this mention of "uniqueness" is because of Jakkard's main exception to our normal rule: guns. On any other plane, where such artifacts of death and destruction might be limited to a certain subgroup (like, say, the Rakdos or something), then it could probably be ignored. But on Jakkard, part of the main focus of the plane itself is the widespread use of guns. I think, if this were a more "normal" M:EM plane, like one of Sertaria's continents or Adrisar or Ihn Gallad, a decent exception could be made to say that this experience isn't far beyond what a canon planeswalker might go through on a canon plane. However, the fact that guns are used by pretty much everyone on Jakkard works against it in this case. Gideon being the main "hero" character among the neowalkers also counts against it (as it is my understanding he even stopped his mission for Eldrazi because of the big Dragon's Maze plot).
So, in the end, I think that Jakkard specifically cannot be said to be visited by canon 'walkers; unless and until we get a canon plane with widespread use of guns (specifically and not just equivalent tech) (and even then limited to only the 'walkers who show up to said hypothetical plane).