Are diplobacillus physically connected?
I couldn't find anything about diplobacilli, but I did find some information on Streptococcus pneumoniae, which has been extensively studied. S pneumoniae (R6 strain) normally occurs as diplococci. Electron micrographs—see here and here—show that the two cocci of a pair share a portion of cell wall. This is a result of incomplete separation during cell division. Also, mutations in peptidoglycan-hydrolysing enzymes have been shown to produce longer chains of cocci.
Presumably, something similar holds for diplobacilli.
Calling these bacteria 'multicellular' might be inappropriate, because multicellularity implies at least some division of labour: the cells perform different functions in a cooperative manner. Diplobacilli (such as Moraxella lacunata) or diplococci have not been shown to have such a division of labour, as far as I know.