If the character who is learning the spells has, or (in this case) can gain, the magical ability that is required to successfully use that magic system, then they would be able to learn that magic. Magic that relies on innate talent cannot be used by characters who do not canonically have that innate talent.

As you mention, it would of course be necessary for the character learning to put in a reasonable amount of time to study and train in the magical system, similar to what would be needed for that type of magic to be learned in its home canon.