One of the most prominent twentieth-century Sarmatian scholars, the Polish historian Tadeusz Sulimirski, supported that position; but I don’t know to what extent he was influenced by personal and national bias. (After WWII, for instance, he used the supposed Polish-Sarmatian connection to advocate Poland taking all German territory that had once been part of ancient Sarmatia.)

It’s sometimes asserted that the Sarmatian Alans spread into Poland and became the ruling nobility over a subject Slav population there, but I’ve seen no modern support for this claim that doesn’t ultimately go back to the work of Sulimirski. The evidence in contemporary Roman sources is scant: just a single mention that a joint Alan-Goth force defeated some (presumably Slavic) Antes while they were themselves being pushed out of the region by the incoming Huns. On the other hand, the Roman historian Ammianus Marcellinus describes the Alans as a non-heterogeneous people, all claiming descent from the same ancestors; and he says they kept no slaves, which one would expect them to do if they were the rulers of a subjugated foreign population. Furthermore, later sources describing the early Slavs report that the Slavs had an egalitarian society with no aristocracy or nobility at all, which seems incompatible with the idea that there was any continuity between the later Polish nobility and a hypothetical ancient Sarmatian ruling class.

On the other hand, ancient geographers did label Poland (as well as everything north to the Arctic Ocean) as part of Sarmatia—but I suspect this is just because they were ignorant of the peoples living beyond the Sarmatians. (This is also the region where they placed clearly imaginary tribes like the Hyperboreans and one-eyed Arimaspians.)