TL;DR: Theoretically, yes; applicably, no.
What I'm going to say may be a little confusing depending on how you view chords. Classically, chords are built with maj/min 3rd intervals. You can construct a whole scale by following the pattern of switching between maj/min 3rd intervals. Say in C, the major would be C, E, G. CMaj7: C, E, G, B. CMaj9: C, E, G, B, D. CMaj11: C, E, G, B, D,(this is a little weird because it's a minor 3rd interval) F. CMaj13: C, E, G, B, D, F, A. If you were to condense a CMaj13 chord and play it in a linear fashion, it fully creates the CMaj scale. So, if the melody is inside the scale, which 99.99% of the time it is unless you're playing jazz or some impressionist piece, it will technically be in the chord. However, it's not safe to assume the melody will simply be in the CMaj triad simply because it the harmony. One way to really bring out specific sounds is to play a maj/min 3rd an octave apart. Play a C and G with your left hand, and an octave higher play E in your right. This really resonates the sound and makes it stand out more. This technique can be applied to any note of the scale, with any chord of the scale, really.