Yes, it is okay to pay bloggers, but depending on what they are blogging about and what jurisdiction they are in, there may be some disclosure requirements.
For example, if you are asking them to review or write positive things about a company, product or service and pay them, some jurisdictions require that it be disclosed that it is a paid advertisement or otherwise indicate that the article was sponsored content.
Another example is if you provide the blogger a free product or service to evaluate, the blogger should disclose they received a free product or service. This often can be done simply by the blogger thanking you for providing a free product or service to try out within the article. You look generous, and it meets the disclosure requirement.
If you are asking a blogger to write something that is not promotional in nature, then no disclosure is required, unless there would be a perceived conflict of interest by not disclosing it.
Example of perceived conflict of interest: The Pork Board paying a blogger to write negative things about chicken. Although it is not promotional in nature, there could be a perceived conflict of interest, since pork producers benefit indirectly by decreased sales of chicken. Not disclosing that the article was sponsored by the Pork Board would be misleading.