Can you reconstitute dried morels in broth instead of water?
The only reason I can think of against it is that your dried morels will have dirt in them and will contaminate your broth.
After the mushrooms have been re-hydrated, pick them up careful from the broth (they usually float).
Then, strain the broth using a coffee filter or a fine mesh strainer (@moscafj).
Use the remaining broth for your risotto.