Quite the contrary!There is no way the US would let them buy Chinese aircraft.
USA won't really mind Ukrainians buying J-10.
First because it won't happen, since China will more likely sell the versions with AL-31 engines, which the Ukrainians are more familiar with. And this would be almost immediately blocked by Russia.
Secondly, if China sells J-10 with no Russian made components, this will complicate Sino-Russian relations. Making both parties distrust one another. China is NOT stupid. Strategic relations with Russia is by far more important than what little gain it would be from Ukrainian purchase. So this is most likely an one-sided Ukrainian PPT, without any real intentions to sell from China.
Of course, there are the third situation, in which China has secretly conjured a plan beforehand with Russia, to provide the J-10CE with a Russian engine, in order to entrap Ukrainian air force into increase reliance on Russian-supplied main components. This is also not very likely because I don't think the Ukrainians are that stupid to be trapped by this.