Hi Krzysztof,
Actually, when you have a querier at site A, queries generated by this querier are not carried over to site B, you will need a separate querier in site B.
As I have recently learnt, in case you have a unicast transport, OTV will craft a dummy PIM hello on the Internal interface so that the switch (or a VDC) will have a mrouter port towards OTV.
HTH
Rgrds,
Miro