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.
