The equal armed cross has been a pagan symbol in a great many early cultures, even when it isn't an ogam. I think its just coincidence the ogam for a-ailm is a cross, all the ogam are straight lines crossing a fixed lines, one to five, crossing one side or both, straight or at an angle. On the stones the meridian line they cross is the edge of the stone.

http://www.wulflund.com/images_items/sun-wheel---mikulcice_2.jpg

Usually thought to represent the sun divided into four by solstices and equinoxes.

http://lh5.ggpht.com/_L2g8S_lz9CE/SH6oHwt_OnI/AAAAAAAAAhM/nj-WkKReAdI/IMG_4440.JPG

Hoping to get signed back to work today, so less stonehead-bothering from me!