You can put Olark on as many web sites and pages as you wish. No need for multiple accounts as long as your operators can field all the resulting chats.
The chat box will also look the same and follow the same rules/behavior that you have set up from your account settings across all pages that are sharing the same Olark account.
You'll be able to tell which site the chat is coming from in the operator chat box where you'll see referring URL. You can also use Targeted Chat to set a rule to give a specific nickname to chatters based on referring URL
If you have a site that uses subdomains, you'll want to also check out our guide for adding subdomains to your settings.