After installing the server, yes, it is possible to recover the MD RAID array. There are plenty of guides to do this online if you search for mdadm and reassemble which are the right words.
Essentially you want to first check that the array is there on boot by looking at cat /proc/mdstat which should reveal the /dev/mdX name, and which devices are in the array, and what kinda of array. For example, this is an active RAID 5 array on /dev/md0 comprising partitions across drives /dev/sdd4, /dev/sdb2, /dev/sda0, and /dev/sdc1.
alan@earth:~$ cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [linear] [multipath] [raid0] [raid1] [raid10]
md0 : active raid5 sdd[4] sdb[2] sda[0] sdc[1]
8790402048 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
bitmap: 8/22 pages [32KB], 65536KB chunk
Yours may look different, but that's roughly what you should get.
If you don't, you can use the following command to scan (but this shouldn't be necessary as I believe Ubuntu will scan on boot).
sudo mdadm --assemble --scan --verbose
Once you have the device name, you can test mounting it with a simple sudo mkdir /mnt/array && sudo mount /dev/md0 /mnt/array and check out the files in /mnt/array. If that's all good you can add an entry to your /etc/fstab to mount on boot.
