Go for it
I agree that H1 holders can submit I-134; just make sure that their bank statements, H1 papers, tax papers and employment letters are attached.
I have read of 1 case where the consular officer asked for the immigration papers of the I-134 sponsor.
If they make this an issue [just because it is a green card case]; they usually give you time to find an alternate sponsor after your interview, so long as your other paperwork is okay.
By the way, as a J-1 holder I submited an I-134 for my mum when she came on a B-2 visa and as an H-1 holder, I submited an I-134 for my brother when he came on an F-1 visa.