If you mean, you don't know if it's save to use asar and xkas on the same ROM, then I don't think thats a problem.
At least I've never had any with doing that.
Correct; the only compatibility issues that you need to worry about are patches that hijack the same address. (Which you'd still have to worry about even if you use only one assembler.)
Basically, using different assemblers on the same ROM is just as harmless as using different hex editors on the same ROM.
Oh, and I can't show the code right now, but I ripped HDMA from Yoshi's Island with a tool, then inserted it with uberASM. It works fine in ZSNES, but in any other emulator, when a dynamic sprite comes on-screen, the HDMA glitches out like hell.
I keep getting an error message while patching any UberASM patch that reads "Missing org or freespace command. Define !addr not found. Errors were detected while assembling the patch. Assembling aborted. Your ROM has not been modified."
I assume you want to directly insert UberASM codes with Asar. Don't do this. UberASM codes are supposed to be inserted with, guess what, UberASM which is either in tool format or patch format. I recommend the latter since most of our resources are build for the tool and not for the patch and using the latter might be a bit difficult for beginners.