Libgdx has support of iOS platform too and our java lib will work on iOS build of libgdx.
I would suggest to use libgdx for iOS build using App42 Java SDK.
We have not tested compatibility of our SDK for robovm yet. If you still want to try with it, you can go ahead and test it by your own using our JAVA SDK.
Let me know if it helps.
Thanks
Ajay