So far as I am aware, if the profile that you use as a starting point is a DNG V1.3 (aka LR3) profile, all should be fine, even if you use the resulting profile in LR4.
However, if you try to use a DNG V1.4 (aka LR4) profile as the starting point for the DNG profile editor, the results may be unpredictable, as the current DNG profile editor doesn't understand DNG 1.4 profiles correctly.
But possible Eric will come along and add more specifics.
Sandy