Melt 2 tablespoons butter in a small skillet over medium. Whisk in flour; cook, whisking constantly, until roux is a light blond color, 1 to 2 minutes. Scrape roux into a separate small bowl; set aside.
Heat oil in a large Dutch oven over medium. Add crushed red pepper; cook, stirring constantly, until fragrant, about 30 seconds. Add corn kernels, celery, shallots, thyme, salt, and black pepper; cook, stirring occasionally, until shallots and celery are softened, about 5 minutes.
Stir in chicken stock, potatoes, and Old Bay seasoning; bring to a vigorous simmer over medium-high. Reduce heat to low, and simmer, stirring occasionally, until potatoes are just tender, about 8 minutes.
Stir roux into mixture in Dutch oven; cook over low, stirring often, until chowder thickens and flour taste is cooked out, about 5 minutes.
Remove from heat. Stir in heavy cream and remaining 2 tablespoons butter. Gently stir in smoked salmon. Garnish chowder with scallions and Old Bay seasoning.
