Can I use an open-drain NXP 74LVC07A output as level translator for an 8V CMOS input?
You're kind of in a gray area. The output should not break down until you get to more than 6.5V and you only need 5.6V for a reliable Vih with 8V supply. Remember that "limiting values" aka "absolute maximum" are not intended to indicate where the part should be operated continuously for reliable operation. The recommended maximum output voltage for normal operation is less than 5.5V. Ignore that at your peril- only you know what the consequences of a failure are. It's also better to drive the 4051 inputs right to the rails otherwise the current draw of the 4051 could go up. 

You could use a couple of SOT-23 or smaller dual pre-biased BJTs (transistors) rather than the 74LVC07A and avoid any possible problem. That's what I suggest doing.. the ones I linked above are good for 50V and are quite compact, but there are many others.