A small shoal of Giant danio's (5, 6 or 7 individual's), are an impressive display in anyone's opinion.
They are certainly speedy enough to stay out of harm's way, in particular avioding the friendly ol' Oscar. There's a fair chance your Red devil will take one here and there as the odd appertiser, but as mentioned, they are relativly inexpensive.
In my opinion the suggestion of some floating foliage is not a good one. These will simply hinder the Danio's effort's to escape a hungry cichlid. Leave them out.