Illegals are always counted for reapportionment purposes; this is not something new for this census.
The Constitution requires that apportionment be based on "the whole number of persons in each State" (14th Amendment, section 2). Nothing in there about citizens or legal residents.
Ummm ... the relevant portion of the 14th amendment states “Representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State, EXCLUDING INDIANS NOT TAXED.” (capitalization mine)
Many illegal aliens are, in fact, Indians not taxed. Lest you dispute that they are Indians, I refer you to the common claim made by many Hispanics that “we didn’t cross the border, the border crossed us.” In other words, THEY believe they are Native American (as, in fact, they generally are). The numbers of Native American persons who are not taxed (i.e. the vast majority of illegal aliens) is specifically excluded from being used for apportionment of representatives. The language could not be more clear on this point.