Hello Matej,
Hope you are well.
Answering your questions in line:
Is it allowed to install cumulative updates for this SQL Server version?
Pedro: Yes. CRM team is not able to test all SQL cumulative updates. We simplify the compatibility by enforcing the boundaries of the Major SQL version, which on this case does allow you to Install any SP or CU higher on sql 2016 , above what the compatibility matrix suggests. The minimum builds are a strict requirement though, both on CRM and SQL.
Do the updates affect on support that is guaranteed by Microsoft?
Pedro: The above answer applies here. Updating SQL server 2016 to latest CU does not affect supportability on your crm v8. Specially since SQL team does complicate support when customers are not on latest SPs/CUs.
Will CRM work OK if we patch our sql server to version SQL 2016 SP2 CU17 without upgrading CRM application?
Pedro: Yes. Any problem that this may cause, should be discussed with SQL support first.
Can we expect any problems after upgrade?
Pedro: Expectation is that no problems will be created by the upgrade.
Note: Build 8.2.2.112 is known to hold a defect that may affect performance on "power users" since there is a table that keeps growing and affects these users forms loading and similar. If you need to know if you are affected by this please check the following SQL query:
Select len(RecentlyViewedXML) as size, objecttypecode, ownerid, s.fullname from userentityUIsettingsBase u
join SystemUserBase s on u.OwnerId=s.SystemUserId
order by len(RecentlyViewedXML) desc
If the top users show hundreds of thousands on length, you are affect and you should open a ticket with us for the mitigation.
The issue is resolved on builds 8.2.3 and above but there is a mitigation if the upgrade cannot happen.
Let us know if you require anything else around the topic.
Thank you!