Does the vampiric embrace proc spell override a weapon's natural proc?
 

As in the spell that necromancers and shadowknights get that gives their weapons a lifetap proc

No, vampiric embrace (when cast) is a buff rather than a proc... so your weapon will still do whatever its doing with its proc on top of that.

Nice, does dex affect the prog rate of vampiric embrace?

Yes

It doesn't affect your weapon proc. I can (and have) proc'd my epic DoT and the VE proc from the same swing.

pretty sure you cant proc 2 things on the same swing. Was probably a double attack and one swing missed but proced.

On live it was a chance to proc each thing so like if weapon proc did not fire then a buff proc could but both could not proc on the same swing.

its worth keeping up regardless if you can or cant double proc