Can the Nexus 7 LTE connect to 3G networks? Is it possible to connect to 3G networks with the Nexus 7 LTE? Is it possible with an unlocked device or only with limited networks or standards? 

I've tried to Google it but no one seems to have ever mentioned it, except maybe a few people asking the exact same thing as I am now...

I've seen this question, but it seems to be highly outdated.
Depends on network provider.

From Nexus 7 2013 LTE Variant Available Now for $349:


  Keep in mind that you won’t be able to fall back to Verizon 3G at any time, but you can fall back to AT&amp;T and T-Mobile HSPA should you choose their service.


From Google's Nexus 7 with 4G is now available in the UK:


  Buying from O2 is a different story, however. The mobile operator is selling the new Nexus 7 for £319.99, complete with a free SIM and 2GB of 3G data.