Not the best sewing job for sure, but on any mount the stitches will be visible if you look hard enough i.e parting the hair.
When I was doing taxidermy my biggest gripe was from customers who wanted me to put an 18 inch caped deer on a 22 inch form. It can be done with enough stretching but the seam will most always open up as the cape dries and shrinks. Luckily the hair running down the middle of a deers back is relatively long [as AT hiker stated a ""mane"] and can be combed over hiding the stitches and seam. This taxidermist also didn't pick the hair out of the stitches very well.
It's actually pretty normal for the seam to open up a little as it dries and shrinks, how much it shrinks depends on the method the cape was tanned or preserved. A commercially tanned and thin shaved cape will typically shrink less than a shop tanned cape that hasn't been shaved thin. Even worse in my experience is a cape that has been "preserved" with a dry preservative.
Hair slippage on the back of the ears is often caused by improper field care. Or not getting the head frozen or caped out and salted down where refrigeration is not available. It could also be from rough treatment by the taxidermist.
I've had deer come into my shop that actually stunk after being thawed out. Evidently they had been left unrefrigerated for far too long and were literally beginning to decompose. Not much can be done with a cape in that condition except to saw the antlers off or make a Euro mount out of it.
If your happy with the rest of the mount, [ear pose, eye expression, etc] then a slightly open seam that can't be seen when it's hanging on the wall shouldn't be too big of a concern. I'm not saying that it's ok for a taxidermist to hide unprofessional work but sometimes he only has an "iffy" cape to work with and he can't perform miracles.