The answer to your questions are maybe, and yes.
lsblk will hide empty devices -- however, in its case, it is only talking about partitions, not the data on those partitions. lsblk is not the best tool for the job here.
This does, however, tell us the partition is not mounted - so yes, it is not currently being used.
So, is there any data on the partition (and therefore, the drive)?
We can find this out with the df command, or disk free.
To view the contents of the partition (and because there is only one partition, we can call this the contents of the drive itself), we first need to mount it.
Let's create a directory for it, as root
# mkdir /mnt/xvde1
And then mount this partition
# mount /dev/xvde1 /mnt/xvde1
Next, before we get to viewing the actual information... let's see how much (if any) disk space is being used. We know the partition is ~ 40GB large, but that's the allocated space, not the used space. [thanks to @n.st in the comments for suggesting to use the partition as an argument to df!]
# df -H /dev/xvde1
Will tell us how much space is being used. Here is an example from my filesystem
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 43G 15G 29G 35% /
The second column (15GB) is the used amount. this is what we're looking for! If it is > 0, this drive is not empty!
You can view all of your mounted filesystems' information by simply using
$ df -H
We use H for "Human readable", by the way. Try it without H and you'll see everything is in K blocks!
And finally, we can view all of its contents (filenames at least) by using:
# ls -R /mnt/xvde1