YES..you can run run tacacs and radius on a same router..Just configure different aaa lists (scheme) for radius and tacacs and use it accordingly..I can't find any exact sample config which dicsuss that but here is the way..
aaa new-model
aaa authentication ppp rad-auth group radius
aaa authentication ppp tac-auth group tacacs
interface
encap ppp
ppp authentication chap rad-auth
for radius and you can use "ppp authentication chap tac-auth" for tacacs authentication..
Tejal