I think to reliably receive updates, it's best if there's a channel with a peer, but you may have to ask John Cantrel and the LDK team about that. Sensei had some similar thoughts around collecting gossip in a single location. Also look at the gossip server that the LDK team created (forgot the name ATM). Their discord/matrix would be helpful to ask them.

if you're not set on LDK, look into immortan. it's a light node implementation that makes certain design decisions to improve deliverability https://github.com/nbd-wtf/immortan

I don't believe you need channels to receive gossip. You probably just need peers which are probably established in an implementation dependent way. It looks like with lncli connect you can tell your node to peer with someone without creating a channel then you can use lncli queryroutes to get a payment route to a node. You can probably call queryroutes over rpc.

This doesn’t address your question directly, but there’s an open lnd issue tracking separation of the gossip subsystem among other attempts to chip away at the monolith. You may find something useful in there, or in the issues roasbeef links to in a comment.

Isn't Neutrino bundled with lnd?