Here is some of the Republican Party platform of 1860. What part do you think John Brown would have a problem with?
7. That the new dogma that the Constitution of its own force carries slavery into any or all of the territories of the United States, is a dangerous political heresy, at variance with the explicit provisions of that instrument itself, with cotemporaneous exposition, and with legislative and judicial precedent, is revolutionary in its tendency and subversive of the peace and harmony of the country.
8. That the normal condition of all the territory of the United States is that of freedom; that as our republican fathers, when they had abolished slavery in all our national territory, ordained that no "person should be deprived of life, liberty or property, without due process of law," it becomes our duty, by legislation, whenever such legislation is necessary, to maintain this provision of the constitution against all attempts to violate it; and we deny the authority of congress, of a territorial legislature, or of any individuals, to give legal existence to slavery in any territory of the United States.
9. That we brand the recent re-opening of the African Slave Trade, under the cover of our national flag, aided by perversions of judicial power, as a crime against humanity, and a burning shame to our country and age, and we call upon congress to take prompt and efficient measures for the total and final suppression of that execrable traffic.
10. That in the recent vetoes by the federal governors of the acts of the Legislatures of Kansas and Nebraska, prohibiting slavery in those territories, we find a practical illustration of the boasted democratic principle of non- intervention and popular sovereignty, embodied in the Kansas-Nebraska bill, and a demonstration of the deception and fraud involved therein.
The point remains that there is no evidence that he was active in the Republican party or supported Abraham Lincoln.