Keep in mind that harddrives have a certain sector size. Writing normally goes per sector, so you should expect lower speeds below the sector size. In additionn most raid configuration either apply mirroring (same data on multiple disks, speeeds up reading as information only needs to be read from 1 disk instead of X disks, however writes have to go to all disks so are limited to the slowest drive), stripping the data between drives (some data goes on disk 1, some on disk 2, reads and writes both would be faster), parity drives, or a combination of these techniques.
Yes, it is possible for a raid configuration to have effect on the speeds. However normally speaking this would speed up read in almost every case (exception might be parity disks) and can speed up or slow down write speed.
In the case of striping you might get a better speed when you write or read from 2 sectors which are on 2 different disks.
Your write speeds seem pretty normal, what I do however notice is much slower read operations. On most drives the speed of reading is normally faster than writing information.
Perhaps the host does not directly actually perform the writes, but rather stores them and slowly writes them out (buffered, either by the OS/VM software, or disks with large cache's or even hardware).
Needless to say however that the test results will not be accurate, with multiple virtual machines running on the machine speeds might be effected by cache's, cpu usage, disk usage etc. Besides that you are writing to a virtual disk which might just store write operations and apply them later.
Without any information on the resources being consumed on the main machine and no information on the sector size and raid configuration it's impossible to say if this is normal or not.