Severance money could not be rolled into an IRA. You could contribute the normal maximum contribution for the year, but that is all.
However yes, the IRS will know exactly where it came from. If its retirement money you will be issued a 1099-R with a distribution code G to indicate that its a rollover. The IRS will get a copy of that 1099 as well. If the termination money is not actually pension money, then you may get issued a W2 for that, which would make it earned income.

