If it worked it would be done all the time. But iroko, unlike teak, develops a myriad tiny surface checks when left exposed and unpainted, so what you get is not a grey deck which goes brown when wet but a black deck which goes black when wet.
Personally, I would cover a marine ply decl with glass cloth and epoxy, and have watertight, light, low maintenance deck, but that's just me being unreasonable again.
I have used Iroko around teak planking Cover boards comings etc, and it works and looks good. It might depend on if you intend to leave it unfinished or use sealer.
