[AngelicaDeAlquezar]

I agree with Rusty that the verb "oler" always takes "a" and the preposition is the same with the noun (and also related nouns)...

- Aquí huele a cigarro. ¿Quién ha estado fumando?
I sense the smell of a cigarrete. Who has been smoking here?
- El aroma a lavanda es relajante.
The scent of lavender is relaxing.
- Tus calcetines apestan a patas. (Mexican slang)
Your socks stink like dirty feet.
- Estas galletas saben a naranja.
These cookies taste like orange.


...unless you're "defining" a smell (same case for the taste of something).

- El olor del cigarro me da náuseas.
The smell of the cigarrete makes me sick.
- Me encanta el aroma de la lavanda.
I love the scent of the lavender.
- Ya báñate. Hueles a la peste de tus calcetines. (Mexican slang)
Take a shower now. You stink like your dirty socks.
- El sabor de las galletas me recuerda a las que hacía mi mamá.
The taste of the cookies reminds me of those my mom made.


For the example without any context, I'd say that "olor a corrupción" sounds like the speaker is qualifying a business that seems illegal, but probably hasn't been quite proved yet. If they had chosen to say "el olor de la corrupción", there is no doubt that there is something illegal; it's plain to see, and this corruption has a wide scope.