vB3 And Photopost Pro Integration Question
 

Is there a way to integrate existing vBulletin user login installed on a different server and a photopost pro installed on another server?

If your vbulletins server's mysql allows external connections you can define an external info and use it when installing your photopost sure.

Is integrating User Login + Stylesheet Integration + Enhanced Forum Integration also applicable to vB3 and Photopost Pro installed in a separate server?

Just want to be sure about this.

No you can not use the enhanced features that would require access to the vbulletin files which you do not have access to when installing on separated servers.