Yes, Oryx can take anything that is living and has a will, so the splicers Fallen apply. However, Oryx isn't taking SIVA. He's just taking the Fallen. As we can see from the current Taken, any armor and weapons that victim has remain with it after crossing the Veil. So Taken Splicers would have a different appearance and weapons than the regular Taken Fallen, but the abilities would be the same. This is because of the way Taking works. When something is Taken, the Darkness speaks to the victim directly, eroding their will as they becomes slaves to the perfect, final shape. That is, to say, the Deep itself. The Darkness corrects a fundamental flaw and/or fear of the victim, resulting in its "perfection." This form of "perfection" is higher than the Devil Splicer's definition, so the abilities would be the same. This is because fusing with SIVA does not convert their existing weakness into strength, they simply improve upon their existing strengths. So, to answer your question, yes, Spliced Fallen could be Taken and their abilities would be the same. The only difference would their physical appearance and weapons.