A seaborn palette is a simple list of colors. You may obtain the colors via

cmap(np.linspace(0,1,cmap.N))

Complete example:

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import matplotlib.colors as mcolors
import seaborn as sns

df  =pd.DataFrame({"x" : np.random.randint(0,4, size=200),
                   "y" : np.random.randn(200),
                   "hue" : np.random.randint(0,4, size=200)})

u = np.unique(df["hue"].values)
cmap = mcolors.LinearSegmentedColormap.from_list("", ["indigo","gold"],gamma=0.5,N=len(u))

sns.swarmplot("x", "y", hue="hue", data=df, palette=cmap(np.linspace(0,1,cmap.N)))

plt.show()