Example:

I got two DNS smart proxies foo and bar.
foo handles the zones foo.example.com and 2.0.192.in-addr.arpa.
bar handles the zones bar.example.com and 100.51.198.in-addr.arpa.

Now I create three hosts:
huey - domain foo.example.com, subnet 192.0.2.0
dewey - domain bar.example.com, subnet 198.51.100.0
louie - domain foo.example.com, subnet 198.51.100.0

As far as I can tell the current behaviour would lead to the following situation:
For huey both DNS entries will be created via smart-proxy foo
For dewey both DNS entries will be created via smart-proxy bar
For louie both DNS entries will be created via smart-proxy foo

The last one - louie - will fail, as is isn't possible to add a PTR for subnet 198.51.100.0 in zone 100.51.198.in-addr.arpa through smart-proxy foo.
Foreman should decide which smart-proxy to use for adding the reverse DNS record based on the configuration of the subnet.
Additionally Foreman should skip the reverse DNS record when no dns smart-proxy is configured for the subnet as this means there is no way for foreman to manage the PTR record.