First base is just such a weird position to try to quantify defensively. I like UZR in general but I tend to apply it to just outfielders and non-1B infielders, where there are far more opportunities for plays to be made and perhaps more precise data on how often a given batted ball is converted into an out, since a lot of 1B defense involves being on the receiving end of a play by another infielder.
I honestly can't answer your question because I don't know how I would judge a first baseman's defense using a sabermetric. Maybe DRS, if I had to pick one (where Abreu is at -4, which seems accurate). Honestly, and this is coming from a sabes guy, I would use the eye test for 1B defense. In my opinion, Abreu is a below average 1B defender but putting him out there isn't gonna severely hurt your team, like putting Palka out in RF would. I do think that he is a lot better than people think when it comes to scooping/picking bad throws. But he's certainly nowhere near as good as Freeman, Belt, Rizzo, etc. defensively. That's something that fangraphs would also agree with.