Immigration and Nationality Act as part of 8 USC 1325, "Any alien who (1) enters or attempts to enter the United States at any time or place other than as designated by immigration officers, or (2) eludes examination or inspection by immigration officers ... shall ... be fined under title 18, United States Code, or imprisoned..."
18 USC is our criminal code. Everything it it applies to crinimal offences. Thus if it applies to a person's case, he is by definition a criminal.
An illegal alien marries a US citizen or starts a business is not automatically committing a felony; those statutes apply to people who marry fraudulently, or people who start a fake business to deceive immigration officials.
And nowhere it says that all illegal aliens are committing federal felonies for the mere fact of entering illegally.