I think MLG is a competitor to ESEA.
Was ESEA LAN stream littered with advertising? I honestly don't remember that much advertising when watching the ESEA stream, so I don't think there's a sponsor conflict and I'm sure that ESEA would be fine not scheduling during MLG events. I don't see them as competitors because of the smaller number of ESEA sponsoring and advertising (free stream for LAN too) while MLG is run by advertising and MLG spectator/stream passes. I could see the conflict, but it doesn't seem like a big deal yet.
tf2 for mlg 2012
Does MLG do online tournaments/seasons or is it all LAN?