I've developed a modbus tcp/ip slave library using those lower level functions of LV (also supports RTU and ASCII modes) so yes, it's quite possible. (I'm thinking of releasing it as shareware but for now we just use it in our own software projects.)
Datasocket is able to use modbus so that's one available solution.
There's some free modbus master libraries lying around too and there are commercial solutions available, including from NI.
Check out these links:
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/2cd034f223c650e9862569570041995c?OpenDocument
http://zone.ni.com/devzone/conceptd.nsf/webmain/DF8C0A4BA2E2B22A86256A3700592BEA?opendocument
http://digital.ni.com/alliance.nsf/0/86B40F30917CED74862563B1006E8CDC?opendocument&vid=
niwc&node=123215_US
http://www.ewebsite.nl/eng/html/modbus.html