Two bookings on the same checkin date causes problems in relation to earning points. The Accor system can't even cope with a booking for a day room in one hotel followed by an overnight stay in a second hotel. As the Accor system records them as overlapping points will be removed on the second booking even though a booking in these circumstances doesn't contravene the ALL T & C's. In such circumstances Accor customer service once they accept you actually stayed in both hotels on the relevant date have to manually override the system and post the points on the second stay to a dummy date which you don't have a stay for. From experience trying to get Customer Services to understand it is possible checkin to 2 hotels and use both on the same date is an uphill task.

If points on both stays is crucial what you suggest won't work.

If having a longer continuous stay attracts a better rate then assuming your friend is a UK resident staying in a UK hotel ID won't be required to check and I wouldn't expect a problem. I have done this for UK hotel stays previously, I normally just email the hotel in advance to explain the second guest will be arriving before me and therefore I would like them to facilitate their arrival. Probably not possible though in countries where some form if photo ID is required due to government regulations.