Can Apple Numbers customize a conditional formatting base on other cell?

Yes.

1) Create a column which will be hidden. in the example above its B.

2) In, this soon to be hidden column, insert a formula which changes the value of the cell to match the value of the cell that you want to conditionally change. In the example above the formula states (IF A2 has a value of less than 40, then the value of B2 is changed to the same value of C2)

3) For the cells that you want to set conditional highlighting rules, add a rule which compares its own value to the value of the hidden cell. In the example given, if the hidden text in B2 matches the text in C2 then the rule changes the color of the text in C2 to gray.

4) Now hide the "Hidden" column. Any value entered in column A less than 40 will change the formatting in column C to Gray Text.

Cheers,

Isiah Davenport