Can seals be used for energy that can be used for basic costs?

No, seals cannot be used to generate energy.

According to the RiftJudge FAQ (specifically FAQ #2715 and #2245), seals generate Power (the colored resource), not Energy (the colorless/numerical resource).

• Energy is generated by exhausting runes and is used to pay the numerical energy cost in the top left corner of a card.
• Power is generated by recycling runes or activating seals and is used to pay domain-associated power costs.

Because seals produce power and not energy, they cannot be used to pay for the basic energy cost of a card. You must still exhaust runes to generate the energy required for those costs.