I am thinking of joining the Sovryn bounty campaign. So I will ask you directly, because I can see that there are many doubts.
If I have an ERC20 address created in Myetherwallet, will I receive a reward in SOV to that address, or not?
Not until you go through the steps to connect your metamask to RSK mainnet.
You will not be able to receive SOV onto the Ethereum mainnet (which is likely your default position for metamask)
You will need to connect to the RSK mainnet which is simple enough.
When you want to use ETH again you switch between RSK and ETH mainnets easily with one click. Infact in my expecrience the wallet often prompts you that you are on the wrong blockchain if you forget to switch