well yes and no. if you don't use anything from the standard class library (that's impossible) than not. what I also guess is that you need a java compiler, since it reads that it uses a ibm created "rom file" that comes from java bytecode.
what the most interesting thing about that vm is, is a shared class cache. which is like a *.so file, if one program loads a library and the library is already in memory another program won't add additional memory to the computer, this is a huge win, especially for memory hungry java applications (this already speeds startup extremly)
I mean ecj is also not included in openj9, so if you want to strip out any openjdk dependency one would need at least a really basic class lib and a compiler (either ecj or anything else), (but I also think it hears that openj9 includes a compiler https://www.youtube.com/watch?v=96XoG6xcnys at the end he only says that they use the class library from openjdk, but he does not say if anything else and it also looks like it only uses that).
To be more precise, a compiler is required for JSP, which is a mixture of html and java that is compiled to servlets.
Theoretically you can compile them ahead of time (before deployment) but as far as I can tell no-one does.
No IBM has its own full JDK that you can download, but the rest of it other than the JVM is not being open sourced at this time. That's my understanding at least.
J9 actually has its roots in an earlier Smalltalk VM (VisualAge Smalltalk, I think). The source copyrights go back to 1991. Eclipse, of course, was what IBM started after abandoning VisualAge.
It's not a JDK/JRE. J9 must be combined with OpenJDK to be able to run apps.