I checked using 'Open in' with Notion and Symphony Pro (on iPad) and Sibelius and Musescore (Mac) and they show up. I do not know what device you are using as GuitarPro is available on different platforms (I presume iOS because you posted in this forum).
Although it is a standard, some apps support (and interpret) more elements of music XML than others. I would check with GuitarPro's tech support to see if they should show on your device.