If a pilot takes a MEL checkride and later a SES checkride, is the pilot now also qualified for MES/SEL? *Assuming all checkrides are passed.

If a pilot gets a multi-engine land rating on a primary checkride, and later takes a checkride as single-engine sea, is the pilot now qualified for multi-engine sea and single-engine land? 

I suppose an unspoken question would be, does a multi-engine rating automatically allow for single-engine PIC privileges, or is the restriction between single and multi-engine a 2-way street?
No. You must take the training and pass the practical test for each add-on rating. See 14 CFR 61.63(c).