i use the same charger and am not sure that a multimeter is going to help you (much) -- once the charger indicates that the battery is "full", you can use the center button to toggle through various statistics for the batteries (including voltage and charge capacity) the charger charges each battery separately and reports on each battery's individual condition. The enloops are great batteries for this and should simply show as fully charged in the m10 once you load them. For piece of mind, I'd a) recharge the enloops before every show (even though they're low self-discharge, I'd let them sit partially discharged until you need them and then recharge as needed) and b) keep a fresh pair of "normal" aa batteries with you so that you can handle the unexpected should the m10 not report that it's completely full . .. .
Returning to the multimeter, a battery's voltage is only part of the equation, you're also looking for how much power it can put out at that voltage, etc. Especially with NIMH (if I'm remembering things correctly), the battery stays real close to its fully charged voltage until it's nearly discharged. So, checking voltage may well not give you the info you need
d