It is probably a good thing to ask question whenever safety is an issue.
The saving grace in this case is the convex mirrors you are talking about spreads light over a larger area in contrast to a concave mirror that concentrates the light (UV). In effect, it increases the "distance" between the light source and the viewer.
The intensity of light decreases at a rate of the distance squared if the distance is in the line of sight. The convex mirror spreads to light over a broader area, so in essence, it increases the "distance" between the light source and the viewer. There are formulas to calculate the intensity of the light, but without knowing the distances from the light source and the mirror and the radius of the mirror, and the distance between the mirror and the viewer, no definitive answer can be provided.
In any case, there is still a chance someone exposed to the UV can receive an arc flash if they are exposed to the UV long enough or if they look at the mirror long enough.
In my humble opinion, it [url=]isn't [/url]a good idea to place a mirror, flat, concave, or convex, above a welding station unless it has the necessary UV filters in place. There is little difference between the mirror and having a galvanized sheet metal roof. Working in the same area as a welder under a galvanize sheet metal roof will still give you an arc flash, it just takes a little longer.
Al