HI Colin
A 25amp ESC fed via a 10amp fuse should not have blown before the fuse. Personally I fit a large fuse in my battery lead sufficient to cover all the amps required by whatever equipment I have chosen to connect. As an added precaution I also fit a fuse between the motor and ESC rated at less than the ESC Max current. This assumes that The correct grade of wire is fitted to carry the current carried. The fuse should always blow before the maximun wiring current is reached.
Many ESC's have a maximum voltage, is it possible that you were exceeding this with your set up? Fully charged batteries will give a higher voltage prior to the full load being applied, and this is sufficient to blow an ESC.
If this is a recent purchase ESC it could have been faulty!
Yes you can and probably should fit an ammeter to test the current and watts. I purchase a wattmeter from GiantCod now GiantShark for about a tenner. Designed for testing LiPo setups but works fine with NiMh's in wattmeter mode - mines good for 100amps. You only need to connect during set up.