Hi, BeKo,
The first difference that IMAQ Remove Particle will not change the shapes of the particles which are kept. They remain exactly the same shape as those found in the original source image. IMAQ Morphology (Erode operator) will change shapes of all particles (and small particles will be disappear, of course).
The only question: which particles will be removed by IMAQ Remove Particle and IMAQ Morphology (Erode operator). If inside of IMAQ Remove Particle NI has used Morhology, then both should be the same. But may be not. You can do simple test yourself - just prepare test image with different shapes of the particles, perform both opearions and compare results.
Andrey.