Technically, the SEP IRA and the Traditional IRA are the same type of account. The only difference is that the SEP IRA is allowed to receive employer contributions. Therefore, you can combine the SEP IRA into the Traditional IRA without any ramifications. When doing so, move the assets as a (nonreportable) trustee-to-trustee transfer.
Whether a conversion is good for you depends of your financial profile. In general, if you can afford to pay the taxes that would be due on the conversion and your tax bracket during retirement will be higher than your tax bracket now, then it makes sense to convert your assets to the Roth IRA. That may sound very general, but only someone familiar with your finances could make a specific recommendation.
At a minimum, you can combine the SEP and Traditional IRA to reduce any administrative and trade related fees that may be charged to the account.
For more insight, read The Simple Tax Math Of Roth Conversions.