This series of iMac's was the start of OS-X. You could first run a dual boot between OS-9 & OX-X. Later on with the newer OS-X versions for the PowerPC you could run a VM for OS-9 apps within OS-X (Classic Environment).
So simply put yes, you can run OS-9 apps on this system if the system has OS-9 setup.
You are limited here to Panther (10.3.9) as the highest version of OS-X and for OS-9 the last version was 9.2.2. Just remember you are stuck with what you have for apps and you would need a newer version of OS-X to used anything in the Apps store which this system can't support.
I don't recommend using this system on the Internet as Apple has stopped maintaining it so it could be susceptible to trojans and the version of browsers for this release don't support the newer HTML code most sites are using today.