Is the "antenna aperture" the same as the "hole in the shield"?
Antenna Aperture refers to the area of radio waves that is equivalent to the power that is obtained from a given antenna. This is always smaller than the physical size of the antenna since no antenna can extract all of the RF power that passes through it. It does not refer to physical aperture but is called that due to the similarity to the aperture of a camera, the larger the aperture the more power is received from a given intensity of radio waves/light and in both is basically a measure of the efficiency/sensitivity.

However a generalisation of the concept could be applied to what you are talking about, you could create a similar metric for the amount of power that passes through an aperture of a given size in terms of an area of the source field. That would give you an "effective aperture" which would be useful in calculating the power that will leak in but except for very simple apertures it is something you would need to measure to have a accurate result. Though when you are designing RF shielding you do not normally use anything like the accuracy used in designing antennas, since it is not very hard or costly to make something much more effective than is needed.

I googled some pages that might help, I only just skimmed them though to see if they looked useful:
http://incompliancemag.com/article/the-basic-principles-of-shielding/
http://www.compliance-club.com/archive/keitharmstrong/design_techniques4.html
https://interferencetechnology.com/analysis-shielding-effectiveness-board-level-shielding-apertures/

Even if it's not a problem you might as well just stick some aluminium tape on it if you have some lying around.