When a male uses a dht blocker does that mean that instead of excess testosterone converting to dht it will convert to estrogen? is blocking dht safe?

Not really: Free serum testosterone remains circulating and available for binding to receptors whether 5-alpha reductase mediated dihydrotestosterone conversion occurs at the prostate and hair follicle cellular level or not. The one potential issue I have in using oral 5-alpha reductase inhibitors in young men (male pattern baldness indication) is a potential reduction in sperm count.

Yes (maybe): As you noted, 5ARIs (alpha reductase inhibitors) block conversion of Testosterone into Dihydrotestosterone. However, as a consequence, you might convert T into Estradiol (estrogen). This is real concern w/potential side effects such as gynecomastia, loss of libido, erectile dysfunction listed in small print for drug. There have also been reports of infertility. Only u can decide if benefit > risk