In general, not really, but the most common string comparison instruction in x86_64 leaves the last character of one of the strings being compared with the other one just being a pointer into the C-style string.

Typically not, but only because they are not typically accessed frequently.

I think you're asking this question because you're wondering if a container that uses environment variables for its configs would show up in this and I think the answer would be no because it's an operating system service that supplies the answers for the values, but every developer on Earth copies the values into variables where there is going to be a pointer put on a register at some point which then would make it vulnerable