In the BDG, White tries to develop and regain his pawn(Nc3 is the most common way to do this) while Black tries to hold on to it or let White waste a tempo regaining it while attempting to out-develop White.
In the Scandinavian, Black usually plays Nf6 and after Nc3 c6 would be a solid move, because if dxc6 then Nxc6 and Black has an edge. But if White plays d4 in the Scandinavian and Black then plays Nc6 it can veer off in a wildly different direction from BDG.
Conclusion:In both openings, both sides try to out-develop each other, but the Scandinavian can quickly turn to something else altogether, while the BDG stays roughly the same.
Is the Blackmar Diemer Gambit similar to the Scandinavian Gambit in terms of theory and imbalances?
I am a fan of the Scandinavian Defense as a surprise weapon in tournament play, but right now I feel like I have no similar openings to use for white .... Well that was until I encountered the Blackmar Diemer Gambit, in the Scandinavian Gambit I normally find myself up in development and a pawn down but after taking (1. e4 d5 2. d4 dxe5) I shortly found myself in a role-reversal. At first I was annoyed that I didn't just go transpose into the Caro Kann once I saw 2. d4, but now I think it my have been luck that I encountered this intresting opening for white. As white I usually play 1.d4 or 1.Nf3, so I would not be on uncommon ground.
Note: I want to know if the BDG is similar to the Scandinavian Gambit, not that either is unsound. I use the Scandinavian Defense as a surprise weapon, so it is not the only response I have to e4 (I use it in addition to the Caro Kann and the French Defense, who all can transpose into on another).