That is an interesting question and not one I have seen.  I don't recall ever seeing an official recipe for using dehydrated fruits and making them into jam or jelly.  That said, it wouldn't be a safety issue to experiment and see how it turns out.  Prunes are a high acid fruit.  You would have to reconstitute the prunes and then mash them using an immersion blender or food processor to make the pulp.  I would think the color would be rather dark and not sure what the taste or texture would be.  
I would suggest doing a little experimenting by redehyrating the prunes and maybe using apple or orange juice for a better flavor rather than water.  Then I would suggest making a butter out of them rather than a jam.  You could try a small batch and see if you like it.  Rather than processing it in a boiling water canner you could just refrigerate it.  The link below has a basic recipe for fruit butter.  You can reduce it to make small batches.  Also gives options for cooking down the butter.  
https://extension.oregonstate.edu/food/preservation/fruit-butters-sp-50-304

I have not tried prunes but I have reconstituted apples and pears and blended them in my food processor, added sugar and cooked down to make a tasty spread.  They are more colorful than dried prunes would be.  

Do a little experimenting and see if you like it.  I like to cook down my butters in the microwave.  Bring to a boil and then reduce the power stirring often until it reaches the thickness you like.  

Good Luck
Thanks for using Ask Extension 

Nellie Oehler