What happens if an item is supposed to seal a skill type, like magic, but you have a skill whose database skill type is Special Skill but is setup as Magic through your script? Currently, your script would allow the actor to be able to use it from either the Special Skill list or the Magic list even though Magic is sealed. Conversely, in the same situation where Special Skill is sealed, you would not be able to use it from either the Special Skill List or the Magic List. Is that what you want? It seems like an odd design choice.
Aside from that, the script seems fine. I have two compatibility concerns though. Firstly, I would suggest that when aliasing a method, you should account for the possibility that another script will change the arguments expected in your method. Secondly, even though you alias, I would be a little concerned since you automatically return true if your condition is met, and if this happens then the original method will never run. That essentially means that any script above yours in script order will not have its conditions run if your condition is met. Ie. if I were to write a script where I didn't want to include a skill in the list if, for instance, it was unusable, then if my script was above yours, it wouldn't operate in any of the skill lists for the types that are added through your script.
Additionally, you don't account for the possibility that nil will be passed to the include? method. That said, it likely wouldn't be, but since that is accomodated for in the original method, I would be cautious about overriding that protection.
Also, why did you choose to use a module? You aren't mixing it in anywhere, and it doesn't seem to be for namespace or for organizational purposes.
All in all though, not a bad job.
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