I would not want that bug on my tomatoes, but I am not sure what effect it will have on MJ plant. I have been up all night and cannot recall the name of the bug, but I like to err on the side of "No" bugs in my grow. Maybe someone with better memory can help you identify the bugger. Peace :)
Boxelder. There are hundreds of thousands of them in the PNW and they are looking for places to winter over right now. Harmless to plants but very annoying.
That bug on your plant is a Largidae and it is a family of insects within the order Hemiptera. They are commonly known as bordered plant bugs because many have contrasting coloured edges to their elytra. There are fifteen genera and about one hundred species. They are mostly wide-bodied, have no ocelli and have a four-segmented rostrum. The bugs in this family are generally ground-dwelling or they scramble around in plants, bushes and trees. They are phytophagous, feeding on plant juices and seeds. Including cannabis but only cause issues in swarms or large infestations nothing to really worry about.