Opera reformats it's content through a server before sending it to the iPad. Because of this it changes the properties of the web pages it views; and that is probably why you can select and copy when using Opera but not Safari. Because the site is accessed via a server (not directly) Opera will also handle some protocols that Safari on the iPad can not, like Java. This also affects things.
Private company sites and other app like sites often use protocols and plugins not supported by Safari, or most other mobile browsers. Is it possible your company just updated the site? I know that OWA (Outlook Web Services) has to be configured properly to work with mobile devices, and if they ran an update it may have changed some settings.
Also (don't remember if it was mentioned) be sure to go to Settings > Safari and clear out your history and Cookies. Also go into the Advanced settings and clear any Website Data for your company's domain.
Or,
If Opera Mini does the job, use it.