If I am understanding correctly, you sent coin to ACINQ, and upon this transaction confirming, they opened a LN channel with you that involves you having outbound capacity in the amount of the coin you sent (less any fees they are charging you), and possibly some inbound capacity for you.
All correct!
If this is true, there is no risk to ACINQ because your "deposit" has already confirmed. Allowing a LN transaction to be processed when the opening transaction is unconfirmed is opening up risk to the counterparty to the channel only, and no one else in the LN network. This is probably a setting that should be set to "disable" by default though.
At first, I was very disappointed they opened a channel with such a low fee.
When I found out I could just use the channel, I was pleasantly surprised. Even though it's more or less custodial until the channel got confirmed, from a user's perspective it's very convenient.
If you are sending them coin in advance, you are giving them custody of your coin before they open a LN channel. This is true regardless of if they open a channel with a fee of 1 sat/vByte, or 10000 sat/vByte. I assume they are taking the fee out of your channel balance, so it will be beneficial for you to have the fee they pay on the funding transaction be lower.