Popeye:
I would say that's an underinformed conclusion, partially because the white/black Chinese population is relatively small, so you don't see them in photo ops very often...
I'd suggest you to read the latest revised Chinese law regarding military service, in Chapter 1, section 3:
It states "All Chinese citizen, regardless of ethnicity, race, occupation, family background, or degree of education, have the full right to serve in the military."
PLA did have two ethnic Russians serving as 1-star generals in the army back in the 60s:
Here's some other examples of PLA soldier of Russian descent:
[qimg]http://i1.hk/u/attachments/day_090423/20090423_83d4e68528280d68ea82chJKb5K9sIcr.jpg[/qimg]
PLA Soldier:
Yes, as what I said above, you can join PLA if you become a Chinese citizen. If ethnically Russian Chinese can join the PLA, I'm pretty sure an ethnically Finn Chinese can do the same. Plus it's all in their consititution.
Hope this helps!