If they are illegal they aren't citizens.
The source material (The Old Dominican study) doesn't use the term 'illegal'. It uses the term 'non-citizens'. The OP uses the term 'illegal', because he's intentionally trying to infer that these were illegal aliens voting. The source material never says this. And strongly suggests this isn't the case. As these folks overwhelmingly had ID. And ID generally wasn't issued to illegals in 2008.
Meaning that the non-citizens we're speaking of are almost certainly legal immigrants. Who are issued ID.