If I'm not mistaken at difficulties above 10 a 10-ch no longer has a guaranteed chance of solving a block.
What do you mean? Right now the difficulty is at 10.22630489.
If jhprimeminer says "10-chain count: 1," aren't I supposed to get credited for 9.55 xpm?
Only if the block found is larger than the difficulty, 10.226.
Look at the top line, eg. :
Best/Max diff: [ 10.067480 / 0.000000 ]
10.067 chain is not considered valid as its below current diff.