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Here you have some general thoughts:

1. First of all, cache jQuery elements (var $this = $(this); instead of multiple executions of $(this)). http://jsfiddle.net/tomalec/pXPdS/1/

2. You can also chain jQuery methods, it simplifies codes, and helps with above.

3. To reduce amount of code you can use toggleClass instead of addClass removeClass.http://jsfiddle.net/tomalec/pXPdS/2/

Here you have some general thoughts:

1. First of all, cache jQuery elements (var $this = $(this); instead of multiple executions of $(this)). http://jsfiddle.net/tomalec/pXPdS/1/

2. You can also chain jQuery methods, it simplifies codes, and helps with above.

3. To reduce amount of code you can use toggleClass instead of addClass removeClass.http://jsfiddle.net/tomalec/pXPdS/2/

4. Instead of selecting $('#rankDrag') in start callback you can use reference given in arguments ui.helperhttp://jsfiddle.net/tomalec/pXPdS/3/

5. To get id of empty/not empty holder ids, in my opinion, .map is more readable than .each. Moreover, you can move that function outside rearrange to avoid re-declaring it every time.

    function getTruncatedId(index, element){
    return element.id.substring(14);
    }
    function rearrange(dropid) {
    //..
    emptyHolders = holders.filter('.holder-empty').map(getTruncatedId);
    isRanked = holders.filter(':not(.holder-empty)').map(getTruncatedId);
    //..
    }
   

http://jsfiddle.net/tomalec/pXPdS/4/

6. Pass dropped element to rearrange, so you will not have to traverse through DOM again:

    rearrange( $(this).attr('id') );//dropId = $(this).attr('id');
    //..
    isEmpty = $('#'+dropId).hasClass('holder-empty');
   

http://jsfiddle.net/tomalec/pXPdS/5/