Does anyone know:
Do Your choices made at the end of LR has any influence to the ending of main game ? Kind of could have - I think ....
Unfortunately I use a mod which allow to continue gaming after Hoover Dam - so I can't test it myself (without replaying all).

It depends on what you mean I havn't tested the ending slide show since the DLC. But since you become instantly vilified unless you go before crockers mission or invitation to the fort all NCR and Legion missions will be lost unles you wear faction armor but even then alot of people can see through disguises.