When the checkbox is checked to 'Use LiteSpeed', when you click 'View T-SQL' it uses the LiteSpeed extended stored procedure, slssqlmaint. Uncheck that box, when you click 'View T-SQL', you'll see it uses the native SQL script. Checked or not (i.e. LiteSpeed or native SQL), runs of the maintenance plan will still show up the same in the LiteSpeed UI.
Using a combination of LiteSpeed and native SQL generated backups, no risk. Nothing special happens. The LSN chain remains the same no matter what created the backups.
Only LiteSpeed can restore LiteSpeed backups and native backups. The SSMS can restore only native backups.
You can't use LiteSpeed templates to generate native SQL backups. You could use LiteSpeed's extraction utility to create a native SQL backup from a LiteSpeed backup generated by a deployed template.