Yes. They are achievement measures, but since what one is often advocating for is access to further academic tasks, they do have relevance. And since every school acceleration involves a curriculum, measuring how one performs in the actual curriculum to be used is likely the most straightforward way of predicting whether one will perform well in the same curriculum. Also, unlike the norm-referenced achievement measures we usually discuss here, they are not transformations of age- or grade-based z-scores. They are actually what we call criterion-referenced measures, where the intent is not to determine one's ordinal standing in the population, but to determine if a specified set of learning standards has been mastered. This has direct relevance for instructional placement decisions, as schools can say with confidence that a student demonstrates mastery of the (say) grade two math curriculum, which is the prerequisite for advancing to the grade three math curriculum. On standard score-based achievement tests, the design is typically to sample skills sufficient to determine one's rank order in the norm population, without necessarily indicating which skills are mastered, and which are gaps. That's why they are not recommended for progress monitoring.

I understand your frustration regarding high fluid reasoning and how that applies to academic placement, but one also needs to consider that the tasks for which one advocates may or may not be well-aligned with fluid reasoning strengths. Honestly, moving up to third or fourth grade math is not going to result in much of a fluid reasoning bump. What you are describing is more like advocating for math advancement based on math ability. The school is countering based on grade-level achievement (which is, of course, directly and likely causally related to lack of above-grade-level math instruction). But since you've introduced her to some of the concepts that she wouldn't necessarily have been able to derive vocabulary for, and the remaining math skills in elementary are essentially all variations and extensions of the four basic arithmetic functions, working her way through math placement tests would, in fact, be a way of demonstrating to the school, in their language, that she has above-grade level math achievement, and thus above-grade-level math instructional needs.

If, instead, they do recognize her above-grade-level math skills, and the issue is that they feel no obligation to instruct any child above the top of the grade level curriculum, then you have a thornier philosophical and advocacy obstacle before you.

And, as a technical note, PP's comments regarding not using interpretations like top 1 in 10,000 with the SBLM are correct. You can only use ordinal descriptors (standing in the population) of performance with deviation IQs. Not ratio IQs like the SBLM.
...pronounced like the long vowel and first letter of the alphabet...