Hard to say chemically and scientifically, but just in my experience the answer is no, for oil additives at least.
I owned an "E" type Jag for 15 years, got talked into putting a very expensive "liquid teflon" additive into the engine early in my ownership, I had the sump and head off to do timing chains after a few years of running, found the "additive" just sitting in the bottom of the sump, in its own stratified layer like a sludge, hadn't mixed at all well with the engine oil and seemingly never drained out properly with oil changes. Never used additives of any sort since then, oil, fuel or anything except what a manufacturer calls for, except I always use full synthetic engine and gearbox oils, (but that's a subject best stayed away from on here). Use the best quality oil in the recommended range spec'd by the oem you can afford is a good policy.
Your inlet manifold is only subject to incoming air, to remove deposits it may be better to remove the manifold and give it a caustic bath to remove the baked on crud, as we used to do with our ancient two stroke motorcycle exhausts back in the 50's, before "low ash" two stroke oils were developed.
Additives could come into the "smoke and mirrors" area.
