In most use cases, there would be no ambiguity. The context will generally rule out the strictly correct option if you talk about prices or actual quantities :

> Cette maison coûte un million deux.

Cannot mean but €1.2M in France, same with :

> Il y a trois million huit habitants dans cette ville (= 3.8M inhabitants).

*Un million un* sounds a little odd, *un million cent* is more common to mean 1.1M.

Same for *Un million dix* to *Un million quatre-vingt-dix neuf*, they might be too rarely used, if ever, to deserve being mentioned.

When you really want to tell 1 000 001, you certainly can use *un million et un* but with something to qualify last "one":

> Un million et un habitant.

> Un million et deux Euros.

> Un million et quatre unités.

One can also say the unambiguous :

> Pile (ou exactement) un million plus un habitant.