I wouldn't do that personally as it would likely be waisteful. Also, significant arthritis tends to not respond to HA very well (compared to other options).
I've had good luck with prp or prp plus triamicolone for horses that do not respond to steroids alone. I've seen some amazing results with adepose derived stem cells plus prp.
In a joint? There has never been one study or is there any body of evidence that suggests stem cells directly injected into a joint stimulates healing or cartilage generation. There is no support structure/physiology or mechanism to get the cells to differentiate etc.
HA is an anti-inflammatory in the joint. Not as good as triamcinolone but effective. The reason HA+tri only works as long as it did was the metabolic action of arthritis and the fact only the inflammatory pathways were targeted. Was the assumption that HA will act as synovial fluid?
As for binding, yes, Il-1ra and HA can bind. In experiments, HA is used to bind up Il-1ra for a delayed release subcutaneous administration (Bendele 2000). However this is not a clinical type application and it is not as simple as putting HA you get in a clinic with Il-1ra in a clinic.
I have had very good luck with the IRAP done on my horse's fetlock 2 years ago (knock wood). Sound since. In my case there was no combined treatment with HA, no follow-up treatment with HA, nothing at all injected since. My vet did suggest a flax seed supplement for possible prevention and it is either helping or at least not hurting.
Also a friend had IRAP in her horse's fetlock longer ago than mine and hers has stayed sound as well.
I'd go with the IRAP and see how that works for you first; you may want injections down the road but I'd let the IRAP work its magic first. No point paying for 2 things at once and then not really being sure which one of them had an impact.
It's just grass and water till it hits the ground.