Actually depending on what kind of shovel nose it is, you should probably take it back to the LFS. Some can reach over 3 feet in length. If memory serves the regular one still gets close to 2.
But to answer your question no it would not be safe. Again the Oscars are going to grow at a much faster rate than the shovel nose. Shovel noses tend to be pretty slender until they are of "tank buster fish" size, and a adult sized Oscar would not have any problems eating a 6-7 inch shovel nose.
Healthy Oscars in appropriate sized tanks will grow about 1 inch a month.