"Bonds" in LAMMPS are between assigned pairs of atoms
and are permanent (with a few exception like fix bond/break).
If you can assign bonds to the pairs of particles you want,
in your data file, then you can use pair_style granular and
bond_style harmonic, without problem. If you want dynamic
harmonic bonds, between whatever pairs of particles are
close, then you'll need to write a pair_style that computes that
force. Then you can use pair_style hybrid with the new one
and pair_style granular.