Can this product be used over particle board Underlayment?

I've used it extensively in three rooms over OSB particle board, then laid laminate flooring. It's worked very well.

DAP Flexible Floor Patch & Leveler is recommended for use on plywood subfloors or concrete surfaces. As a general rule, we do not recommended the use of our patching/repair compounds on particle boards.

If I am understanding your question correctly ,The answer is YES. I used this to fill in a good size dip (almost a hole) that was caused by water damage. This dip was on particle board that was under carpet that we removed. I was replacing the carpet & could not leave that low spot and bought this to fill it in before getting the new carpet laid. I put plenty on and worked fast so it would not dry one me too quickly before I could level it out. I used a trowel and then a straight stick to make sure it was level , let it dry completely then lightly sanded it down. I worked out great. I had the new carpet put over it the next day and no sign of any uneven spots. It worked well over particle board , just make sure you level it evenly and once dry you can lightly smooth it with sand paper if needed.