I reckon it'll work but you probably need to think as much about spares and adaptors as you do the actual fork.
Assuming you're thinking about a quick change in an emergency, then you probably need to take a bit of a tick sheet approach I guess.
Have you got the same Headset on both bikes? if so then make sure the standby pair are pre-fitted with an appropriate crown race,
make sure your spare forks and both bikes front brakes are easily interchangeable, best bet would be to have PM callipers on both bikes and make sure you have a the right IS-PM adaptor(s) ready if your different forks have different mountings.
Steerer lengths? are both frames similar enough that this won't be a biggy? (probbly not an issue but worth double checking) just make sure you have a few extra spacers just in case there's an extra 10mm of steerer on the spare fork you hadn't remembered...
Any Star nut/preload cap compatability issues?
I assume Axles are all the same size right? If not can hubs be adapted or are there suitable spare wheels available?
As for the differing travel thing, It might make sense to space the Talas down to 130mm just to cover your bases.
Then again another option might be to look for a cheap and cheerful set of older Marz forks in the 100-120 range, remember its just a spare pair so ~£50 for a an old set of Bombers could make sense, or is having 2 sets of spare forks a step too far?