Yes, a series connection will be safe for the amp, however the resulting 16 ohm impedance load will reduce the center channel amp capability from its rated 110 watts to about half or 55 watts. This will then be split between the two speakers. Sound from each LM1 will likely sound thin and anemic, and have very little dynamic range. It makes more sense to run a single LM1 with 110 watts than 2 with less than 30 watts each. A series connection will just reduce the overall performance.
Now I am not against using 2 center speakers, actually if it was safe to do a parallel connection, I would say go for it, however I do not agree with,
You can try it that way but your amp may strain a little.
Initially it might work OK, but long term is likely to cause premature failure. Again, talk to Marantz tech support.