Hundreds of thousands of LineageOS users (myself included) have used the sideloaded Gapps for many years without any issues at all. It all depends on where you source the apps from. If Huawei is now getting the apps and testing them out themselves, the apps should be fine as long as you get them from Huawei (ie. through Huawei's app store) and not via an known 3rd party site.
It is true that Google cannot vouch for the security of apps in Huawei's app store as they don't test them, but let's not confuse users. They could add that if the apps were thoroughly tested by Huawei and it is ensured the apps are obtained from that verified source, they should be fine to use, but again Google is not part of the process so it must be Huawei who vouches for that. Anyway Google's "checks" don't hold a lot of water judging by the amount of malware in their apps that keep getting taken down after the fact... maybe Huawei does an even better job!
Google has released a statement detailing what Huawei’s US Entity listing means for the smartphone manufacturer’s upcoming devices.