Are there any certificates for embedded system developers?
No, not really.  There are some courses you can take, but as a interviewer, I really wouldn't care.  In fact, if someone came to a interview and proudly showed some certificate about having complete a course, I'd immediately suspect he doesn't know anything.  Of coures I'll find out soon enough for sure after asking a few questions.  It's about what you can do, how you think about things, and what you know.  I don't care how that got into your head, only that it did.

That all said, I do look at education level.  I have found from experience that the best embedded engineers have a masters degree in EE.  I don't think their better performance is about the extra education, but about the attitude that caused them to seek the higher degree in the first place.  At the BS level you still find candidates that got there just by going thru the motions.  Some of these may get good grades, which only shows how little grades mean.  Instead of learning electronics and developing some good intuitions and accumulating a few design practises, they have learned how to answer test questions well.  Obviously they don't make good EEs.  By the masters level, these people have been weeded out.

So the bottom line is, BS EE is a must, and masters EE will put your resume to the top of the pile.  If you list lots of other certifications you just make yourself look like a weenie and I wouldn't know what all that alphabet soup means anyway.