I ran into situation where the boot files from our local repo had not yet been published and Foreman still created a host against that OS without any errors or warnings. The only errors were in proxy logs [1]. The boot files ended up on filesystem but as 0 byte files. The host of course failed to pxe boot but it would have been useful if Foreman failed to create a host when the host's OS failed to download PXE boot files.

[1]:
D, [2017-08-10T16:26:18.426452 #20099] DEBUG -- : accept: 10.20.0.1:48050
D, [2017-08-10T16:26:18.452774 #20099] DEBUG -- : Rack::Handler::WEBrick is invoked.
D, [2017-08-10T16:26:18.485405 #20099] DEBUG -- : verifying remote client 10.20.0.1 against trusted_hosts ["<OMIT>"]
D, [2017-08-10T16:26:18.486098 #20099] DEBUG -- : Starting task: /usr/bin/wget --timeout=10 --tries=3 --no-check-certificate nv -c "http://<OMIT>/pub/mirror/rhel7.4-server/images/pxeboot/vmlinuz" -O "/var/lib/tftpboot/boot/RedHat-7.4-x86_64-vmlinuz"
I, [2017-08-10T16:26:18.520726 #20099] INFO - : 10.20.0.1 - - [10/Aug/2017:16:26:18 -0400] "POST /tftp/fetch_boot_file HTTP/1.1" 200 - 0.0673

D, [2017-08-10T16:26:19.302079 #20099] DEBUG -- : close: 10.20.0.1:48050
D, [2017-08-10T16:26:19.338643 #20099] DEBUG -- : accept: 10.20.0.1:48052
E, [2017-08-10T16:26:19.389380 #20099] ERROR -- : [4572] https://&lt;OMIT&gt;/pub/mirror/rhel7.4-server/images/pxeboot/vmlinuz:

E, [2017-08-10T16:26:19.389464 #20099] ERROR -- : [4572] 2017-08-10 16:26:19 ERROR 404: Not Found.

D, [2017-08-10T16:26:19.390643 #20099] DEBUG -- : Rack::Handler::WEBrick is invoked.
D, [2017-08-10T16:26:19.424530 #20099] DEBUG -- : verifying remote client 10.20.0.1 against trusted_hosts ["<OMIT>"]
D, [2017-08-10T16:26:19.425210 #20099] DEBUG -- : Starting task: /usr/bin/wget --timeout=10 --tries=3 --no-check-certificate nv -c "http://<OMIT>/pub/mirror/rhel7.4-server/images/pxeboot/initrd.img" -O "/var/lib/tftpboot/boot/RedHat-7.4-x86_64-initrd.img"
I, [2017-08-10T16:26:19.425614 #20099] INFO - : 10.20.0.1 - - [10/Aug/2017:16:26:19 -0400] "POST /tftp/fetch_boot_file HTTP/1.1" 200 - 0.0015

D, [2017-08-10T16:26:19.428228 #20099] DEBUG -- : close: 10.20.0.1:48052
E, [2017-08-10T16:26:19.452693 #20099] ERROR -- : [4576] https://&lt;OMIT&gt;/pub/mirror/rhel7.4-server/images/pxeboot/initrd.img:

E, [2017-08-10T16:26:19.452824 #20099] ERROR -- : [4576] 2017-08-10 16:26:19 ERROR 404: Not Found.