Im my trade as a boatbuilder i used a lot of iroko, i am always surprised at the number of people who say it is an oily timber. Now Teak is oily but Iroko? maybe if its freshly felled or unseasoned but all the Iroko i ever used was dry & far from oily. Its one of the dustiest timbers to machine & the dust is really nasty. Putting a rough sawn board through the thicknesser without extraction the dust comes off like smoke, I always used a respirator! Finishing i have always just sanded down to 240 grit with the random orbital & on went the varnish first coat thinned down, never had any problems.
If using modern micro porous finishes such as Johnstones woodstain or sadolin i have found that they simply refuse to dry indoors when applied to Iroko. A rowing boat which i did this way some years back was still sticky after 4 days, I put her outside in the sun & wind & the stuff dried as quickly as on any other timber. I have done several similar boats since with same result but I dont think this this is anything to do with supposed oil in the timber. Thats my experience anyway!