For example, can we use the microRNAs involved in specific stress in a plant submitted on mirbase.org as a source for analysis of those microRNAs in other stresses?
Definitely, you can consider the miRNA involved in an abiotic stress condition to compare or to check its regulation in biotic conditions, if any kind of relation exists.
Now, an important thing to note that miRNA which is being listed in the Database are mostly telling about their targets, possible mechanisms, and associated disease since it is being studied and proved. But, the response of particular miRNA under different conditions is a matter of investigation.
For example, a miRNA has a possible role in heart development, found to be involved in cancer progression too. It shows that based on pathological and physiological conditions, miRNA function changes. Possibly by targeting the same gene.
I'm very sure about the possibility of the phenomena, but I'm not a plant expert. I hope these papers may give more ideas.
I think you could use them as candidate miRNAs of interest, and it would be relatively cheap to carry out RT-qPCR on those in your own materials. This would show if they are associated with the conditions you compare or not.
A better option, but more expensive, is to do small RNA sequencing and then expression analysis. It would show any miRNA in your sample that might be associated with the conditions you investigate, not only for the candidate ones.