Boondoggle is correct.. any supplements regardless of brand can kill mosses.. most plants are tolerant to some powder unless you are really caking it onto the plant or are dumping it in the same spot every day.
If you are concerned about the supplemnent affecting your greenery then you can place a petri dish into the enclosure and just dump the feeders plus supplement into the dish and then remove the extra dust later in the day.
I use a jungle pod as a feeding dish.
All excess powder stays in with a bonus if you place a piece of fruit in there. (some flies will congregate around the fruit and may pick up a small amount of vit\cal dust)