Yes, they will work. However, Radeon inside APU will be disabled. I don't know, if this would be cost effective. If I were you, I would rather buy Athlon X4 750K and 750 Ti at the beggining. I'll explain.
Prices taken from my local shops in € (prices will surely vary, but it is easier to explain like this). I live in Europe.
AMD A10-7850K - 160€
AMD Athlon 750K - 70€
Nvidia 750 Ti - 130€.
So. If you buy A10-7850K and later Nvidia 750 Ti, it will cost you roughly 160€ + 130€ = 290€ and you will have disabled Radeon GPU in your PC.
If you buy Athlon X4 750K and Nvidia 750 Ti, it will cost you 70€ + 130€ = 200€ and no system resources would be wasted/idled.
Of course, you would need 40€ more at the beggining, but in the long run, you could save 90€.
Hope this helps.
Have a nice day.
P.S.: Another idea
AMD Radeon R7 250 - 70€
A10-7850K and later Crossfire it with Radeon R7 250. That is 160€ + 70 € = 230€ with no parts idling and still decent GPU performance (though it won't be stronger than Nvidia 750 Ti.)
P.P.S.: I promise this is the last mindblowing recommendation
AMD Radeon R7 260X - 105€
Athlon X4 750K coupled with this card. 70€ + 105€ = 175€ and danger close to Nvidia 750 Ti or even better by few % at most usage scenarios.