Perhaps, but to me it looks like a water-carried distribution of the similar-colored dark stuff splattered around and heaped at the base of the same pipe. And because that heap of red-brown gunk is extremely radioactive and associated with a ventilation/filtration system, it may well be (largely) cesium-vapor residue, which is also dark red-brown.
What we can say for sure is that the stain lines are consistent with some red-brown substance washed down with rain. But that does not entail that it's rust.
Yes I see the tape, it's obvious, but what kind of tape allows rust to fester as you suggest? I don't see why the tape increases the likelihood of the staining being rust. Maybe it's to stop corrosion as you suggest, or then maybe to reduce the escape of cesium-vapor residue in the event of a filtration-system rupture. It might be there for a number of reasons. I doubt we can infer much from the tape being there.