Will bootloader unlocking provide access to all the apps in the Play Store?
No. Unlocking the bootloader will do nothing for Google Play. Even rooting won't do anything by itself as far as phone compatibility goes.

To get access to the apps without device restrictions, you must have a rooted phone. You then must edit the build.prop file to change your phone model to one that can install the app in question. See this android.se question.

To get access to the apps without country restrictions, no root is needed. You must instead have a proxy whos IP address is inside the particular country desired (generally the U.S.). Or you could create an account via a U.S. proxy on your desktop, then push the apps to your linked device despite it's out-of-country location (see this explanation). Alternatively, you could have a rooted phone and download Market Enabler.