Maybe it can work, but you need to test it first.
On the MX, if traffic matches an allow rule on the L3 firewall, it can still be blocked by an L7 firewall rule.
On the MX, HTTP traffic (TCP port 80) to Facebook.com will be blocked by the L7 firewall, because rule 1 under layer 7 explicitly blocks it, even though the traffic was allowed through the layer 3 firewall.
Layer 3 Rules
- Matched - Traffic allowed through L3 firewall
- Not processed
- Not processed
Layer 7 Rules
- Matched - Traffic blocked
https://documentation.meraki.com/General_Administration/Cross-Platform_Content/Layer_3_and_7_Firewal...
I am not a Cisco Meraki employee. My suggestions are based on documentation of Meraki best practices and day-to-day experience.
Please, if this post was useful, leave your kudos and mark it as solved.