"Differential voltage probe" vs "LEM LV25-P voltage transducer"
These are very different products, the LEM transducer is for mounting on a PCB for inclusion into a product, the Tek probe is for attaching to a scope.
 LV25-P provides isolation voltage measurement.
Isolation voltage sounds like a Hipot test, neither of the products will do that. I assume you mean isolated voltage measurement (isolating the measurement device from the voltage under test)?
 I assume "(High-voltage) Differential voltage probe" (e.g. Tektronix product) does NOT provide isolation voltage measurement. Please correct me if I'm wrong.
Both of the probes (banana leads) of the differential probes are isolated up to the rated voltage. Neither of them is grounded (hence differential), and can be connected to any potential within the specified limits.
 If "Differential voltage probe" is safe for high-voltage floating voltage measurement, then why do we need "isolation voltage" measurement like LV25-P?
You can't really integrate a Tek probe into your product, they're probably much more expensive and much larger. But a PCB mounted device isn't very convenient for measurements on power electronics. The bandwidth of the LEM device is probably lower, and so is the rated voltage I think (can't find a spec of differential mode voltage).