I have good results diagnosing problems with the motors on hydraulic units. Misalignment, soft foot, bearing issue etc. The pumps on the other hand have been an aggravation. Almost all of the pumps that I check are piston pumps. Most of the time the number of pistons will show up in the spectrum (good to know how many pistons are in your pumps beforehand). Bearing frequencies are seen, but the trick is which amplitude is high. depending on load this changes drastically. At least in my equipment it does. In my opinion vibration analysis on hyd motor/pumps is worth the time and effort, but does take some time to decide what's good or bad on each unit.