Sure, it makes sense to ask a compiler engineer the various ways in which to reverse a binary tree. That's going to be a problem that you're probably going to encounter on the job.
The fact is that most developers spend 90+% of their time futzing with NPM, dealing with Apple's review process, or renewing SSL certificates. Low-level algorithm work is something very few engineers need to know.
But still, if the other 10% of the time is designing the system, it can wreck the project if you do a bad job at it. And no amount of futzing with NPM is going to save you, no matter how good you are at it.
It also depends on if you want the guy to be more than a front-end bug-fixing guy in the long run.
