If both feeds are identical mono signals that's the right approach, no?
An engineer would do something very weird, he would communicate with you and ask you why you provide him with 2 signals. It's a bad idea to just assume something without knowing. It might be the same signal while patching the lines but different stuff during performance. As an engineer you'd be smart enough to figure that out even before soundcheck.
Just as an example:
95% of the gig it might be the same signal on both lines but in this one song where you grab your acoustic guitar, you might give him dry guitar on the first line and delay/reverb on the second so he can mix it nicely for the given venue.
What I tried to say is that someone who calls himself an engineer should be a bit smarter and not just assume something he doesn't know yet. Or in other words, if he has worked with 9 dumb guitarists in the last month, it doesn't give him reason to assume the tenth guitarist is dumb as well, right?