We can't assume that any given hotel network is well-configured, but most enterprise networking equipment verifies the source of multicast traffic against the multicast routing tables. This means that if you simply send packets with a source address matching the real multicast source, the network devices will ignore and not forward them. This reverse-path check is a standardized part of PIM, the most common protocol that network devices use to communicate multicast groups between each other. It's also enabled by default on Cisco devices for local groups and I would assume the same of other vendors.
That said, it's considered a best practice (although not really all that common) to use ipsec or another method to provide cryptographic authentication of multicast packets. The protocol discussed here may do so.
That said, it's considered a best practice (although not really all that common) to use ipsec or another method to provide cryptographic authentication of multicast packets. The protocol discussed here may do so.