We use 2% paraformaldehyde to fix our cells for flow cytometry. (Usually we are looking at cell surface antigens.)

Does anyone know if 7-AAD staining can be used in conjuction with fixation? I've read both that it can and can not be used with formaldehyde fixation.

If you fix the cells then the membrane will become allow 7-AAD to enter the cell. If you plan to use it as a viability stain, then this will not work. If you wish to measure DNA, then that is another matter.

Invitrogen sells a number of dyes that allow you to stain cells for viability prior to fixation. You can search for Live/Dead stains on their site to see their offerings.