Oh yes, definitely. He would have had her living as a housekeeper, stuck at home all the time while he was out with the boys, hunting and drinking, and refusing to let her go anywhere, forcing her to have tons of sons just for him. I remember in the cartoon, he suggested that they would have 6 or 7 boys just like him (a frightening prospect, such a man creating more of himself). Gaston would have all her books burned, and hit her if he saw her reading anything, even just a letter. On top of that, he probably would have extra female friends in the village that he wouldn't tell her about. So Belle was smart in refusing to marry Gaston. Her life would have been a living hell with him.
Yes Gaston would have treated Belle more like a slave if they married, he saw her crazy just reading books, and he would have argued about how the discipline their kids. Gaston surely didn't accept Belle's differences and he didn't really love her he just wanted a dream come true and thought Belle was his best choice to give it a chance. He probably wouldn't even let Belle look for a better friend with how rude he already spoke to her and his opinions of life, if they married, Gaston's jealousy that caused his anger is quite clear near the end when he fight the beast.