They are both interesting foils for each other, in many ways as well. The biggest one would be how they both interacted with there loved ones in there backstories. Skipping most of the details, the core of there love-lives revolve around whether they followed through with their desires or whether they stayed true with the expectations of the people. Rama stayed true with the people's expectations which he would regret over as it had him to abandon Sita, Lancelot on the other followed through with his desires and he hates himself over it since he believes he betrayed the King's trust and led to the demise of Britain.
Another thing of note is that they both prefer themselves to be in certain classes, even though it limits there abilities. Rama prefers Saber over his more powerful Archer as it allows him to continue to look for Sita while Lancelot prefers Berserker than to Saber as thanks to his guilt he can only see himself as a disgraced and hated knight despite it limiting the use of his NPs such as For Someone's Glory and Arondight. They also clash in battle as well. With Rama being a warrior so skilled he is basically 3 Classes in one while Lancelot is able to become a master of any weapon he holds even in the depths of madness.
I can see them either becoming close because of their similarities or becoming hated enemies for those same similarities. I just think seeing them together would be interesting, well that's what I think.
Also want to see who would win in a clash between the Strongest Knight in Arthurian stories and the Greatest Hero in Indian Myth but I digress.