I definitely fall in the category of kernel newbie, so go find your grain of salt to take this post with.
My gut feeling is that it shouldn't cause much trouble. You apparently haven't changed the needed hardware drivers, or changed the UUID of the real root fs, etc.
"Other distributions (such as Fedora and Ubuntu) generate a more generic initrd image."
What do you mean by "is it safe"? Are you just thinking about system stability? If so, as long as your system boots and then behaves properly, then initrd has done its job once the real root file system is loaded.
If it's peace of mind you're after, why not just compile again using the --initrd?
My suggestion for forum:
Linux - General
This forum is for general Linux questions and discussion.
If it is Linux Related and doesn't seem to fit in any other forum then this is the place.
Now that I've thoroughly messed you up, let's hear from an expert.