9 pole mini din identification
Is this socket standard?

Pinwise, yes, it seems to me that all 9-pin mini din connectors are that way, with an uneven first row, which is also found in the 10-pin model. If there are no differences in dimension, there shouldn't be any problems using a 9-pin din on it. Although that happens to be my experience, the fact that the datasheets indicate otherwise would make me second-guess myself.
Although, it does not seem to feature the two little notches near the bottom, common in the mini din connector, which might make it incompatible.(EDIT: A new picture shows that it does indeed have the notches.)

Are the datasheets wrong?

Well, it seems to me that they could, but it is hard to say, really.  You should look for a datasheet with measurements to see if it really is non-standard.

Could I buy a 10 pin, and just pull one of the pins out of the plug?

I don't think the two bottom row pins would necessary align if you remove the middle one of a 10-pin. But perhaps with some force you could, although it would not be ideal.