Electrolytic recovery is simple and effective, in practice under some circumstances the fixer can be re-used and it isn't harmed at all by the process, but the build up of iodide from film emulsions limits the reuse. If the plating is done at too high an ampage then yes sulphurisation takes place, commercial electrolytic recovery units have circuitry to control the voltage & ampage to prevent this.

Some re-circulating units recover the silver electrolytically from Fixer or Bleach Fix on continuous process machines, allowing slightly more efficient use if the chemistry, however the sophistication of the control circuitry is far higher than for standard plating units, because as Ron (PE) says fixers and particularly bleach fix can be damaged, these units control the voltage and ampage to give a slower rate of recovery.

On an industrial scale spent fixer or bleach-fix is desilvered electrolytically and often used again and again to recover silver from old X-ray & Graphic Arts films. So often when fix solutions are sent for recycling they get used again before final treatment & disposal.

To have a any problem with Hydrogen & Oxygen liberation you would need a very large commercial rectifier to generate the high ampage required, commercial units are designed to cut out well before that point can be reached, as by then the plating process would have broken down anyway.

Small scale recovery from a litre or two of fix using a battery system would be very safe and easy, I would only advocate using a purpose built mains unit. The secret to good plating is to keep the ampage low and allow the silver to plate out slowly, there's plenty written about plating on other websites.

Ian