It can be a good idea to merge them. This is because the Social Capital Theory will focus on the actual 'relationship building' aspect between the individuals/entities (taking all necessary factors into account) whilst the social network theory can act as the ‘enabler’ and can focus more on how such relationship building can be enabled and promoted through both physical and technological social networks. Be creative when combining/mixing them.
Hi Anil, in my article "Measuring the social capital of brokerage roles" (Connections / available here on Research Gate) I discuss the application of concepts from social network analysis in order to measure the social capital of broker roles. This can also be understood as an example of how collaboration between different network clusters functions (see also Ronald Burt in "Brokerage and Closure" on this topic). Take care, Volker
Try seeing if Granovetter's weak ties work for you, if not, maybe Krackhardt's strong ties.
Both concepts are linked to collaboration and you can easily tie them to social networks theory or analysis with basic concepts like centrality and/or degree.