There's always more to be said, but this great answer on racism in the WWII-era Red Army by u/Georgy_K_Zhukov goes a long way to answering your questions. I suspect you'll find his discussion of racism in general more interesting than a direct answer to the rank question.

If you insist on getting a specific upper limit on the rank that Sakha krasnoarmeitsy could hope for, though, there are more than a few examples of them reaching the ranks of Major listed in the National Archive of the Sakha Republic.

(There are two ethnic Russians born in the Sakha Republic who reached the rank of Major General, but I suspect you meant members of the actual ethnicity known exonymously as Yakuts and endonymously as Sakha, so we can forget these two guys.)

And although he didn't reach a rank any higher than sergeant, Yakut sniper Fyodor Okhlopkov counted over 400 kills, making him quite the respected figure.