from the images currently on the rubrica page?

It's funny that your question of B. rubrica vs. B. champlaini comes up right as Tom Murray, Jim McClarin, and I were racking our brains trying to figure out the difference between B. champlaini and B. vagans (see comments under 17189). As if all we needed now was more confusion! B. rubrica has a prominent vertical ridge running down the side of the pronotum. Beyond this ridge anteriorly, the pronotum tapers strongly into a thin neck. In a perfect dorsal view, the pronoton looks cube-like with a sharp corner or step off just behind the thin neck (this is discussed in Dillon and Dillon and Yanega, also look at the upper left corner of the pronotum on the cedar creek image of rubrica). The anterior pronotum of Champlaini has a more gradual, rounded taper that may have some angulation to it but nothing like rubrica. Unfortunately, none of the 4 photos on the rubrica page show the sharp angle so a stickler might say that none could be safely ID'd as rubrica. However, I think they are all correctly identified in that rubrica also tends to have somewhat elongated elytra while champlaini has a bit of a stumpy appearance (compare to photo 17187). In general it should be easy to tell the two apart in that rubrica is much bigger and that the two don't overlap in size. But, and just to confuse things, the only image that includes a size estimate is 22875, which at 10mm is too small for rubrica. Yet, that beetle just plain looks like rubrica to me although I can't prove it to you.

Yes, the squarish anterior corners of the pronotum in Cedar Creek's image of B. rubrica are easy to see, and I agree that none of the images currently on BugGuide's rubrica page show that feature. If a square-cornered pronotum is a characteristic that rubrica should have, then all of those IDs are questionable.
I found images of 3 other genera that look somewhat similar to B. rubrica: Anastrangalia, Gnathacmaeops, and Lepturopsis, plus there's several additional Lepturinae genera (currently missing from BugGuide) that I couldn't find images of, so I think it's possible that one of them has a species that is a better match for the images currently shown on B. rubrica page.

I guess it all depends on what level of certainty you want. I think the somewhat elongate and tapering brick red/clay-colored elytra and banded antennae are most suggestive of B. rubrica in those 4 images. Also, Dillon and Dillon gives a size range for rubrica of 10-16mm (yanega reports 12-18) which makes me feel a bit better about image 22875, reported at "about 10 mm." As for the ridge, D and D state, "a strong carina extends from the apex of the (pronotal) lateral margin toward the procoxa giving the pronotum a subquadrate appearance as viewed from above." I think the key word in all that is "above" because you really need a perfect dorsal view to see a squarish pronotum. In other words, just because the 4 images in question don't show it, we cannot say for sure that it's not there. Actually, the feature isn't so obvious and can be a little hard to see if there is a lot of pollen, etc. Take the cedar creek image for example; you see the corner on the left but not on the right. Like I said before, it comes down to the burden of proof that you want. I think the moral of the story is that contributers should be strongly encouraged to give a size estimate with their photos (which would have helped rule in/out B. champlaini). Also, for Lepturines in particular, a good dorsal image of the pronotum is almost essential to make the most accurate ID but I don't know if you can REQUIRE that. I am no photographer but I can assume that the beetles don't always cooperate!

I think the saying, If you don't see it, you can't call it is a good one to follow.
If "a strong carina... giving the pronotum a subquadrate appearance..." is a diagnostic feature, and we don't see it, we can't call it. There's no benefit in guessing at what can't be seen.