Can two atoms with the same amount of electrons but differing electronic configurations be considered isoelectronic?
$(\ce{Y+})$ with configuration: $\ce{[Kr] 5s^1 4d^1}$ and strontium $(\ce{Sr^0})$ with the configuration $\ce{[Kr] 5s^2}$ are not isoelectronic. In order to be isoelectronic the two atoms would have to have the same electronic structure as well as the same number of valence electrons. 

IUPAC Goldbook


  isoelectronic - Two or more molecular entities are described as isoelectronic if they have the same number of valence electrons and the same structure, i.e. number and connectivity of atoms, but differ in some of the elements involved.