Revenue generation is irrelevant. The payroll alone would necessitate the income tax requirement depending on the work. In many states (not IL) the type of work is ALSO irrelevant for business tax purposes where the tax is an excise or capital based tax. By the way, the exemption for soliciting sales only applies to tangible personal property and not intangible property or services.
The exemption for soliciting tangible sales only applies to income and not franchise/capital taxes. For instance, in MA the OP's prospective employer would be obligated to file a corporate return regardless as corporate excise tax is based on the greater of apportioned income, excise on tangible property in the state, or apportioned net worth.