Hi Chris,
When you have an enumeration of font families in the font-face element, the PDF processor will prefer to use them from left to right.
So if the first font says that it can render a character, it will be used for that. Otherwise the second font will be asked if it can render the character and so on.
So you should probably set Aller as the first font.
After the PDF publishing is over you can also look in the console output received from ANT, it should tell at the end what fonts it uses and if certain characters/glyphs cannot be rendered with it.
One more thing, if you also have the Polish characters both in the titles and in the content, you should also take care of the physical fonts used for the "Serif" alias.
Regards,