Some old (1880s) emulsion formulas I have read about contain no added ammonia at all. Instead, faster variations claiming greater contrast use more NH4Br. This leads me to think that some of the ammonium ions from the NH4Br are acting in a solvent role to produce larger, less disperse crystals. These emusions likely carry a high excess of halide during preciptation and ripening leaving the excess ammonia that didn't combine to form NH4NO3 available as a solvent. All the excess halide is removed during the washing step.
I have also read a more modern double-jet formula that did not use ammonia but rather ammonium thiocyanate which served a dual role as a solvent and sensitizer.
I'd guess that an emulsion ripened without ammonium present would be very slow. Would it even ripen as in growing larger crystals? Or at the end of a ripening phase would you just end up more or less with the crystals you started with when first precipitated?