There is value there, though it is small. To a counter each card has a small value to it, and when they're all put together and the true count is comprised that's when all those small values can add up to something of real value.
If the burn card is 2-6, that's going to start your RC at +1. In a 6 deck game that's 1/6 = TC = .1667, "off the top." So as you can see, small value, but knowing more information is always a good thing.
This wouldn't matter as much to a shuffle tracker with a slug at the bottom of the pile, though if they were going to count the shoe to that point to figure out an even better solution for the slug then it again would matter, just a tiny bit.
If the shuffle tracker is doing the right things and the slug is at the top of the pile, this could effect the slug more greatly though. If they have a 2 deck slug with an RC +8, so TC +4, then this one burn card now affects the TC much more than previously. Say it's a big card (10 value)... RC = +7 on the slug, so instead of TC +4 now you're at TC +3.5. The smaller the slug the more this card would affect the TC.
Playing it correctly means you've already won.