Per the CCNP Service Provider requirements, the certification can be achieved by having a valid pre-requisite (CCNA Service Provider) and passing the required exams: SPROUTE, SPADVROUTE, SPCORE and SPEDGE. Please note that these requirements do not have to be completed in any specific order.
So yes, you can definitely take any CCNP Service Provider exam(s) without a valid pre-requisite. However, the actual CCNP Service Provider certification can only be awarded by fulfilling all of the necessary requirements - Valid pre-requisite + valid required exams.
Good luck to you!
Cisco Learning Network Moderator