This site indicates that suitable tankmates for pajama cardinals are other cardinalfish:
http://saltwater.tropicalfishandaquariums.com/Cardinal/PajamaCardinal.asp">http://saltwater.tropicalfishandaquariums.com/Cardinal/PajamaCardinal.asp</a>
On Wet Web Media, I read "Most cardinalfishes as individuals get along with their own kind, [B]other species of apogonids[/B] and other peaceful tankmates.":
[IMG]http://www.wetwebmedia.com/cardinal.htm">http://www.wetwebmedia.com/cardinal.htm</a>
I think you'd be fine.