To each, their own. If you want to, and like the look, AND can provide the care that each needs, then why not. It says that Ixora are acid loving and are prone to nematodes...

Personally, here in the south Ixora grow to be quite large shrubs. I don't see them together as companion plants, especially since the amaryllis will be dormant for a couple of months...but if it's what you want to do, no one is going to tell you not to. Again, just consider the needs of each.
K

Let me just say that I think the ixora needs more water in the summer than the amaryllis can stand, even with a well draining soil mix. Better to pot them side by side in matching pots since they both like lots of sun.

Thank you both for the follow up. I will plant them separately- they looked pretty all grouped together, but it sounds like it won't work out.