Its partially correct that GNS3/eve-ng run IOL. Both of two can run QEMU images also, which means any thing can be virtualized and CSR is included. You can run as many CSRs as you like along with asa, fortinet, palo alto, windows, linux, F5 ans so many others. Only real limitiation is your hardware specs. I never run IOL for my labs as it seems buggy. I always run IOSv routers and switches.