The IRS doesn't complain if you claim MORE income (or less loss) than what they know about.  Besides, when claiming a loss you are required to attach a Basis statement to the tax return anyways (another thing that ProSeries does not do).

No.  Although some people use Form 6198 as a work-around of ProSeries limitations, that is the wrong way to do it.  Form 6198 is for "At-Risk" limitations, which is different than Basis limitations.