Can the Airtronics 94358 be used with a life rx pack? I had one of my hitecs go out and while I wait to get a replacement I put in my back up servo, but its older and specs are only for 6 volts.

Any servo rated at 6v can be powered by a 2s LiFe pack. The only time you need to be careful is when you are using unregulated 2s LiPo voltage with only 6v serves.