I was trying a few datasets (random data, Iris), but it seems that the Jitter control is not enabled (at least in: Polynomial Regression (Learner), Linear Regression (Learner) with KNIME 2.7.2, Win7, both 64 bit). I think in these cases the cause is that it is not possible to select nominal columns, but there might still be overlapping values. Is this an issue, or this is by design? Do you plan to support jitter with numeric columns? Or do you plan to extend these algorithms in some way to have nominal columns in training columns?
(I think of an acceptable workaround like giving alpha value to the colour of points to see where are multiple items. Do you have better?)
PS.: The Execute and Open Views action's name is a bit misleading as it opens only the first view, not all.