Plums and peaches can be grafted onto each other anyway, so yes, you can graft peach, nectarine, or plum to your hybrid.

".. not sure the parentage of SpiceZee"

If I did the math right, Spice zee parentage is 50% nectarine, 37.50% peach, and 12.50% plum.

K thanks ltheweatherman,
I'll try next year some grafting on it.

here is the patent description
http://www.freepatentsonline.com/PP13503.html

I have been told by a friend that plums do not graft well on to pluots. They seem to take but do not thrive or grow to any significant extent. His pluots have been a failure for him and he'd like to salvage the trees.

That's anecdotal and only one case--and not yours, but I mention it just as a caution.

I suggested he try an interstem of something supercompatible like Myro 29C.

Pluots are basically 95+% plum and I have grafted many plums successfully to pluots.

You can graft plum on peach but peach on plum doesn't always work. Since the interspecific is mostly peach I expect either peach or plum should work on it.

Scott