In theory, the logic of this attribute should be handled internally by NUnit and shouldn't require any involvement from NCrunch. I can't say that I've specifically tested it, but I can't tell you any reason why it wouldn't work. I recommend giving it a try.

Again, in theory, I can't think of anything that would prevent you from writing your own extended version of RetryAttribute. As long as NUnit's code picked this up and invoked it in the same way as the normal RetryAttribute, there is a good chance it will work. I am a little less certain of this one in the sense that extending NUnit in the past hasn't always worked out so well for NCrunch, because it steps into untested behaviour.

This is all under the assumption that you're doing this in NUnit V3.