Ok. Rocket descriptor...
...It literally fires live rockets, inhabited by the souls of murderers and the likes, their faces attached to the front; screaming all the way from the moment they leave the barrel, until they blow up at will when they get close enough to a victim. They use their eyes to determine such, and if they're unable to see someone, they will not detonate themselves until they hit something.
...My invisibility is exactly what it can be at tier 5, not impossible to see but difficult, much like your Predator example.
There is a good chance, perhaps as high as fifty-fifty that the two abilities will in someway negate. It is possible that the shells "see" the shimmering image, perhaps not. Especially as in the post it is clearly stated that
The rocket skimmed past him...
If it skimmed past there is a greater likelihood it could "see" the cloaked spider, perhaps just as it passed him, thus detonating slightly behind but clearly with the Archivist in the blast radius. Will it hurt the Archivist? Dunno but will it have some effect yes. To what degree is up to melon