Among the many things that life sends us to ponder is the question of "acceptable" splice. Brion Toss refers to splices as knots -which, in contrast to some of the writers who have gone to great lengths to distinguish ,knots, hitches , bends , splices , seizings and all other facets of cordage manipulation and affixation, seems logical and healty to me. Splices depend upon friction and mechanics just as all other knots do. We accept that knots weaken rope. The great appeal of splices is that they either permit rope joinings to pass through hardware or in the case of eyesplices are very strong. I think the most accepted minimum figure is 90% strength for an eyesplice-with 100% sometimes obtainable. On the other hand a 65% rope strength knot may be entirely acceptable. My point is this. Practically any cordage can be spliced(a minimum disruption/diameter increasing knot) in some fashion. I suspect that the reason some products have no approved splice is because the manufacturer hasn't found a splice that they deem consistent enough in meeting that 90% strength level. That doesn't mean that an enterprising rope manipulator can't make a union that stays together in normal use. If you "Splice it, stitch it, seize it" most anything will probably hold up to the loadings we normally place on our climbing systems.
No, I'm not advocating trusting your life to someone's improvised splice....unless you choose to. In which case it really isn't my business.