Harlem is as safe as any other neighborhood in the city, but property values have been near the apex for some time so the value is not the same where it was say 3 years back. However, there are different enclaves within Harlem that you can look at for comparison, you have Spanish Harlem, Harlem proper, Sugar Hill, Strivers Row (arguably the most beautiful block in NYC), etc...
Good luck with your search!
Your best resource to obtain the information, would be to contact the local police department. Also, the internet also has sites that report crime statistics for cities throughout the United States so that you can do your research and make a determination.
Good luck in your condo search.