Yes, it is okay to create multiple developer accounts. What we do is that each developer has an Apple developer account and generates their own development certificate. In the main corporate account (the team agent account), we create development and distribution provisioning profiles used by everyone. Apple has a clear and helpful guide on setting up a multi-developer team.
Each dev's certificate is added to the development profile; this means that every dev can use this development profile to run the app on their phones. Xcode will by default pick up their development certificate associated with this profile (if the code signing identity in project settings is set to "Automatic Profile Selector" > "iPhone Developer").
Unfortunately for the distribution profile though, you cannot really add any other certificate except the distribution certificate you created from your corporate account. A simple workaround to this is to just share the complete distribution certificate (public+private key and cert) with any developers that should have the ability to create a distribution build for the app (for a small team like ours, we just share the distribution cert with everyone). You can easily export this certificate from Keychain Access.
Once the dev(s) have added this distribution certificate to their keychain, this too will automagically be selected by Xcode during a distribution build (provided the code signing identity for the relevant build configuration is set to "iPhone Distribution").
Apart from this, I am not really aware of how you can get past the 100 device limitation, since all the devices have to be added to one account (the corporate/team agent account).