Does this circuit have marginal voltage level problem?
However looking through the datasheets I found that MAX9010 outputs
  TTL levels, while 74VHC86 accepts CMOS levels (0.7 * Vcc).


That's a good spot and I agree with you - maybe you should inform Maxim on their dodgy circuit. Shame on them.


  Should I pay special attention to this issue - what are the conditions
  when circuit may fail producing proper clock?


Yes, you can't use those two chips together without lowering the power rail on the 74 series. Maybe try a MAX999 - it's slightly faster on propagation time (4.5 ns) but, importantly, hits the rails on the output hence will drive the 74 chip.