It shouldn't be a problem, they are pressed in so as long as you have the correct installation hole size they will seal well.
That design of PEM style standoff will have a lower pull out factor. Have you looked at the B or BS style? These are used when there also is a requirement to prevent the screws from protruding though the standoff and shorting out on PC boards. There is a video on the PEM site and the link is here: http://www.pemnet.com/design_info/video_library_b_test.html
