In the Table Panel (or control bar with a table highlighted) you can set the cell height to "Exactly" and insert the value you want.
But... you're right.. you can't save this particular aspect to a cell or table style.
To use a style you might try this....
- Create a paragraph style which sets the type size to match your desired cell height. For example, 6pt type for a 6pt tall cell.
- Create a new Cell Style and set it to use the paragraph style you just created.
- Set the Cell Insets in the Cell Style Options to zero.
That should allow you to select a row (or cell) and apply the cell style to get a spacer which matches the height of your predefined Paragraph Style.
Another option would be to simply create a Cell Style with a larger Top Inset to move the cell items down. Basically a taller cell style to create the appearance of a spacer, without actually having a spacer row. This tends to fail if you want to alternate fills or strokes though.