As far as I know, the Robux wouldn’t be credited to your account. As long as:
- The product sold is not made by you, and…
- The game the product is being sold at isn’t yours.
Then no, you would not receive any Robux, even if Developers use your Plugin.
As for other ways to get Robux, there are Premium Payouts, which Roblox credits Robux to your account for a certain amount of time Premium users join your game and play.