Is this possible that one Linux DHCP server in a virtual environment can serve multiple VLANs ????

In IT in general a HUUUUUUUUUGE thing to appreciate is what aspects of an environment relate to what other ones. You've asked about a few different things here, DHCP, Virtualisation and VLAN's. These things really seldom have anything at all to do with any of the other things, in terms of what they actually are. DHCP is a layer 2 protocol, it doesn't know *anything* about VLAN's, it knows about layer 2 and 3 networks. These may tend to be implemented on a 1:1 basis with a vlan (i.e. vlan 123 may well be used for subnet 10.0.123.0) but they are not aware of each other at all. Similarly virtualisation can not matter here either, what if it did? That'd be pretty messed up wouldn't it? Running VMware would suck if you had to run different networks and protocols just because a server is a vm.

So, all that's relevant is whether ISC DHCP can server multiple subnets. And yes it can very trivially. Note though that you need to serve it *directly* on that network. Either by the server being connected to it or by having a relay agent on that network to pass the requests on. You just define the each network config correctly within your dhcpd.conf and give it a whirl.

Yes ... virtualization cant matter here. Forget this.

In my case a small magik-dhcp freeware can serve multiple subnet to multiple vlans on any machine(virtual/physical) but in case of linux dhcp, it is only able to serve the vlan within which it is.

While there is no configuration related to dhcp is enabled in L3 switch which connects all VLANs, the freeware can do things that a linuxdhcp cant.

it can do it. It's part of the DHCP rfc, it's not possible to not be able to do it and still be a dhcp server.