A logo is a graphical element that is used to identify a brand. It can be a symbol made up by text and images. Logos are trademarked, meaning that they are protected by trademark law so they cannot be copied and used by other brands.
Short answer: No, icons cannot be used as logos.
Long answer: We do not allow our icons to be used in logos at all. Using icons from Iconfinder or from our API for a logo is never a good idea and it is also legally problematic. By definition, icons are not unique, whereas logos are original and not used anywhere else. Icons on Iconfinder are protected by license agreements and are copyrighted by their creators. For this reason, you are not allowed to apply a trademark on them, as you would normally do for a logo. If you use an icon for a logo, you will not legally own your own logo and you won't be able to trademark it.
Another solution would be to contact the icon designer of an icon that you like and to ask them to make a variation of it and to sell it only to you. The icon then needs to be significantly different to make sure that you are not going to find it anywhere else. You can send a message to the designer directly on Iconfinder. How to message the designer of an icon