A track loader does not typically provide enough compaction to seal the core trench in a dam, but should provide more than enough compaction to build a stable underwater berm (IMO). Especially if you build the berm in lifts of 8" and spray enough water to provide optimal compaction of each lift.
How stable will your water level be? A clay berm exposed to air during a drought would probably suffer some significant degradation.
How deep will your berm be below the normal water level? If greater than 3', then there will be very little in the way of erosive forces trying to destroy your berm. I don't think you would get much added benefit from adding in the quickcrete.
