Are the social-distancing measures implemented against SARS-CoV-2 also suppressing the spread of other viruses?
Yes, this helps as well with other infectious diseases. A good example is the flu, which season was measurably shorter this year than in other years on record. See the figure from the reference 1 for comparision:



Reference 2 shows that this is also true for other respiratory diseases (figure 2):



This shows very well that the isolation measures and the social distancing work very well to control such transmissable diseases.

References:


How coronavirus lockdowns stopped flu in its tracks
Monitoring respiratory infections in covid-19 epidemics