tried recently to get rtsp stream into vvvv and found on forums that it was quite an old issue..
so if it's not fixed yet in more straightforward way, it may be done by installing dshow source filter, presenting ip stream as virtual videocapture device all over windows (vvvv, skype, whatever).
the only working one of ~15 tested options yet was moonware source filter
you'll need very recent v.5.0.4 from here (sorting out yet watermark-free version)
worked with videoin from imagepack out of the box (neither dx9 nor dx11 videoin alas), beta 35.2 x86.
this one looked promising also, but kinda costy and needs some more c# to integrate as plugin