The reason to unhide the rocket part item, is so that one can make a parameterized blueprint, for example, parameter 0 set as the recipe for the rocket silo, and parameter 1/2/3 for the requester chest requests, set as ingredients of parameter 0. This then allows for selecting the rocket part recipe at the time the blueprint is placed down, and the requester chest can also have the appropriate requests for the quality level of rocket part ingredients.

For this, in data.lua:
data.raw.item["rocket-part"].hidden = false

But I tested it and you can do that! The recipe is not hidden, only the item form is. So you can make a parameterised blueprint of a rocket silo, and when placing it, choose the rocket part as the value of the parameter. Moreover, you can use rocket parts as a signal (e.g. in a constant combinator). What you can't do is make a logistic request for rocket parts, or add a rocket part filter to an inserter/splitter, which makes perfect sense.

(Fyi: the rocket part recipe/signal is found in the intermediate products tab, not the space tab, also the icon has changed recently, it now likes like one of the things in the icon of this mod).
I will update the screenshots in the mod's description to use the new icon.

(Actually you can make requests/filters, if you first open a rocket silo, and press q on the output slot on the right, then you will get a ghost rocket part item!) I've fixed this by just removing the output slot from rocket silos.