If you engage in clean room reverse engineering, probably not.
Some have already done this: look at ScummVM and https://github.com/GTAmodding/re3
Some have already done this: look at ScummVM and https://github.com/GTAmodding/re3
Edit: Also what about possible patents? (Not that I think any were used in SC4)
Note this really only applied for Americans, correct me if im wrong but Reverse Engineering with no limitations is legal in the EU (software patents are also illegal in some parts of the EU, that i am certain of)
https://lwn.net/Articles/134642/
Usually its allowed for interoperability, which is what you are trying to do.