Tiger is 10.4, right?
It should work, as far as I know. Possible problem: MacPorts turns out not to be intended for distributing binaries, but for recompiling on the local destination system. (Yea, that threw me when I saw that discussed on the MacPorts forums). The behavior of putting the MacPorts compiled libraries and frameworks into a program is unsupported at best.
It might be that the stuff compiled for 10.5 doesn't like 10.4; if so, that's ... well, so much for binary API compatibility :-).
<Sigh>. Best I can say at the moment.