You could very easily be seen to be operating a link farm, which could be fatal.
The quick test is "are these links of value to my visitors"; id fyes, then proceded - but either use nofollow, or be prepared to check regualrly and frequently for links that 'go bad', else you risk a 'bad beighborhood'.
If the links are for SEO puroposes or a webmaster service, then the best advice is 'forget it' - it's simply not worth the risk. Even if it didn't raise a flag, a rival may dob you in. And if something serious goes wrong with your site, it's one more issue that might have caused it.